What is Tuna Casserole?

Traditional tuna casserole is a beloved classic American recipe consisting of a delicious blend of ingredients such as cooked noodles, canned tuna, a creamy sayce, and sometimes vegetables. However, I've taken this traditional recipe to the next level by making it incredibly simple to prepare while adding an extra touch of cheesy deliciousness.

Is Tuna Casserole Keto-Friendly?

Regular tuna casserole is not keto-friendly since it's made with pasta and breadcrumbs. Still, fortunately, there are many keto-friendly versions of the dish that use low-carb substitutes such as zucchini noodles and almond flour.

High-Protein Tuna Casserole

Name: High-Protein Tuna Casserole
Prep time: 15 min
Cook time: 15 min
Total time: 30 min
Ingredients: 2 (5 oz) cans tuna in water (drained, about 10 oz total); 1 cup zucchini (finely chopped); 1 cup celery (finely chopped); 1 medium red onion (finely chopped); ⅓ cup mayonnaise; 1 tbsp Dijon mustard; 1 cup mozzarella cheese (shredded ); 1/2 tsp sea salt; ¼ tsp black pepper; ¼ cup fresh parsley (chopped)

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This High-Protein Tuna Casserole is an easy 30-minute dinner made with canned tuna, zucchini, celery, red onion, Dijon mustard, mayonnaise, and melty mozzarella. It’s creamy, cheesy, filling, and perfect for meal prep.

Casseroles are one of my favorite dinner recipes since they are super easy to make using only one dish. Whether you’re craving the classic flavors of a Cheeseburger Casserole, the spicy goodness of a Taco Casserole, or the richness of a Million-Dollar Chicken Casserole, each dish offers its unique appeal. And now, with the addition of this delicious Tuna Casserole to your repertoire, you have even more variety to enjoy.

TABLE OF CONTENTS hide

Why You’ll Love This High-Protein Tuna Casserole
Ingredients You’ll Need
How To Make Keto Tuna Casserole?
My Best Tips
Recipe Variations
Serving Suggestions
Storage and Meal Prep
More Seafood Recipes
High-Protein Tuna Casserole

So if you are looking for an easy and delicious dinner recipe, this healthy tuna casserole checks all the boxes. This dish is both filling and nutritious, made with tender tuna, a delicious blend of spices, and a layer of melted cheese.

Why You’ll Love This High-Protein Tuna Casserole

High in protein – Each serving has about 23g of protein, mostly from the canned tuna and mozzarella.
Great for meal prep – It reheats well, so you can make it once and enjoy it for easy lunches or dinners during the week.
Quick to make – Everything gets mixed in one bowl, transferred to a baking dish, and baked until hot and cheesy.
Budget-friendly – Canned tuna, zucchini, celery, onion, mayo, mustard, and cheese are simple ingredients that don’t feel fancy or expensive.
No noodles needed – This version skips pasta and uses finely chopped zucchini and celery for texture, freshness, and a lighter feel.
Creamy and cheesy – The mayo, Dijon, tuna, and mozzarella make the casserole creamy, savory, and satisfying.
Easy to customize – You can add more vegetables, change the cheese, make it spicy, or use canned salmon instead of tuna.

Ingredients You’ll Need

Once you see how easy and few ingredients are required to make this delicious tuna casserole, you will want to make it over and over again. Here is a list of everything you will need:

Canned Tuna – Use 2 cans of tuna in water, drained well. I like solid or chunk tuna because it gives the casserole a better texture than very finely flaked tuna. Let it drain in a colander while you prep the vegetables so the casserole doesn’t turn watery.
Zucchini – Zucchini keeps the casserole lighter and adds moisture, but it should be finely chopped, not shredded. Shredded zucchini can release too much liquid and make the casserole watery.
Celery – Celery adds a little crunch and freshness. Chop it finely so it softens slightly while baking but still gives the casserole texture.
Red Onion – Red onion adds flavor and a little sharpness. Chop it finely so you don’t get big raw-tasting pieces in the casserole.
Mayonnaise – Mayo makes the casserole creamy without needing canned soup. Use 1/3 cup. This amount is enough to bind everything together without making the casserole too heavy.
Dijon Mustard – Dijon adds tang and makes the tuna mixture taste brighter. Regular yellow mustard can work too, but Dijon gives a better flavor.
Mozzarella Cheese – Mozzarella melts beautifully and gives the casserole that golden cheesy top. You can also use cheddar or a mix of mozzarella and cheddar for a stronger flavor.
Garlic Powder – This adds a little extra savory flavor without overpowering the tuna. If using fresh garlic, use 1 small minced clove.
Parsley – Fresh parsley makes the casserole taste fresher after baking. Add it at the end, right before serving.

How To Make Keto Tuna Casserole?

You will be surprised to see how easy it is to prepare this insanely delicious casserole recipe. Here are the steps that you need to follow:

Preparing The Tuna Mixture

Start by preheating the oven at 400F/200C.

In a large bowl, combine the drained tuna, zucchini, celery, mayonnaise, mustard, chopped onion, salt, pepper, and 1/4 cup of shredded cheese. Use a silicone spatula or spoon to mix all the ingredients together until well combined thoroughly. The creamy mayo and tangy mustard will enhance the flavors of the tuna.

Assemble and Bake The Casserole

Transfer the tuna mixture to a 1-quart casserole dish, spreading it evenly. The dish’s size will ensure proper cooking and allow the flavors to meld together. Sprinkle the remaining shredded cheese on top of the mixture. The melted cheese will create a delicious golden-brown crust.

Place the casserole dish in the preheated oven and bake for approximately 15 minutes or until the top is golden brown. Keep an eye on the casserole to prevent it from overcooking. The baking process will allow the flavors to meld and the cheese to melt, creating a delectable and satisfying dish.

Once the casserole is cooked to perfection, remove it from the oven. Garnish with freshly chopped parsley for a touch of freshness.

Serve the Keto Tuna Casserole while it’s still warm, and enjoy its delightful flavors.

My Best Tips

Drain the tuna really well. This is the most important step. Extra liquid from the tuna can make the casserole watery instead of creamy.
Finely chop the vegetables. The bake time is short, so the zucchini, celery, and onion need to be small enough to soften slightly in the oven.
Don’t shred the zucchini. Shredded zucchini releases more water. Finely chopped zucchini gives better texture and keeps the casserole from turning soggy.
Let it rest before serving. The casserole will look softer right out of the oven, but it firms up slightly after 5 minutes.
For meal prep, cool before storing. Let the casserole cool before adding it to containers so condensation doesn’t make it watery.

Recipe Variations

Spice it up: If you’re craving some heat, try adding a tablespoon of red pepper chili flakes to give your tuna casserole a spicy kick. It’ll add a fiery burst of flavor that’ll make your taste buds tingle with delight!
Get cheesy: Take your tuna bake to the next level by using a combination of your favorite cheeses. Whether it’s sharp cheddar, gooey mozzarella, or creamy Gruyere, the melty cheese will add a deliciously indulgent twist to this comforting dish.
Veggie power: Boost the nutritional value of your casserole by adding your favorite vegetables. Broccoli, cauliflower, and mushrooms are fantastic options that not only provide a pop of color but also contribute to a healthier and more well-rounded meal.
Crunch and flavor: For an extra layer of texture and taste, consider adding crumbled crispy bacon and green onions to your casserole. The crispy bacon will bring a delightful crunch, while the green onions add a fresh and savory note that complements the tuna perfectly.

Serving Suggestions

Even if this keto tuna casserole is enough to create dinner on its own, you can also pair it with various delicious side dishes like:

Cauliflower Rice: Serve your tuna casserole alongside some flavorful cauliflower rice. It’s a low-carb alternative that complements the dish perfectly while adding an extra dose of veggies to your plate.
Fresh Green Salad: Keep things light and refreshing with a simple green salad as a side dish. A mix of crisp lettuce, juicy tomatoes, and crunchy cucumbers will add a burst of freshness to balance the richness of the casserole.
Cauliflower Mashed Potatoes: If you’re craving comfort food, whip up some creamy cauliflower mashed potatoes. It’s a fantastic low-carb substitute for traditional mashed potatoes that pairs wonderfully with the tuna casserole.
Roasted Vegetables: Roasting a medley of your favorite vegetables, like zucchini, bell peppers, and asparagus, will create a colorful and flavorful side dish. The caramelized edges and tender textures of the roasted veggies will complement the casserole beautifully.
Your Favorite Keto Bread: If you’re in the mood for some bread, choose your favorite keto-friendly bread option. Whether it’s almond flour bread, cloud bread, or flaxseed bread, having a slice on the side will complete your meal.

Storage and Meal Prep

Store leftovers in an airtight container in the refrigerator for 3 to 4 days.

Reheat individual portions in the microwave until hot, or warm the casserole in a 350°F / 175°C oven until heated through.

For meal prep, divide the casserole into 4 containers after it cools. Add a simple side salad, roasted vegetables, cucumber slices, or cooked rice if you’re not keeping it low carb.

You can freeze this casserole if needed, but the texture will be softer after thawing because zucchini releases moisture. For the best texture, I prefer storing it in the fridge and eating it within a few days.

Frequently Asked Questions

Is this tuna casserole high in protein?

Yes. This tuna casserole has about 23g of protein per serving, mainly from the canned tuna and mozzarella cheese.

Can I use canned salmon instead of tuna?

Yes. Canned salmon works well in this recipe. Drain it well, then use it the same way you would use the tuna.

Why is my tuna casserole watery?

The most common reason is extra liquid from the tuna or zucchini. Drain the tuna well and finely chop the zucchini instead of shredding it. Letting the casserole rest for 5 minutes after baking also helps it firm up.

Can I make this tuna casserole ahead of time?

Yes. You can assemble the casserole up to 24 hours ahead, cover it, and keep it in the refrigerator. Bake it when ready, adding a few extra minutes if it goes into the oven cold.

Is this tuna casserole good for meal prep?

Yes. It reheats well and makes an easy high-protein lunch or dinner. Store it in individual containers in the fridge for 3 to 4 days.

Can I add more vegetables?

Yes. Finely chopped mushrooms, bell peppers, broccoli, or spinach can work. Just avoid adding too many watery vegetables unless you cook or drain them first.

Can I use cheddar instead of mozzarella?

Yes. Cheddar gives the casserole a stronger, sharper flavor. You can also use a mozzarella-cheddar blend.

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