Cook Bacon and Steam Broccoli- Fry or bake the bacon in the oven until crispy. Meanwhile, blanch the broccoli in boiling water for about 2-3 minutes. Crumble the bacon into small pieces.
Prepare the chicken- Cut the chicken breasts into bite-sized pieces and pan-sear for 5-6 minutes over medium-high heat. You can also use leftover shredded rotisserie chicken breast.
Preheat the oven to 375 F degrees/ 190 C Celsius and grease a 9x13-inch glass casserole baking dish.
Assemble - Combine cooked chicken, bacon bits, broccoli, ranch dressing, 1 cup cheddar cheese, and mozzarella in a large bowl. Toss together until well incorporated. Mix in about 3 tablespoons of ranch seasoning for extra ranch flavor.
Transfer the chicken mixture to the prepared casserole dish, and top with the remaining cheddar cheese and bacon.
Bake for 20-25 minutes in the preheated oven, or until the cheese is melty and the chicken casserole looks golden brown on top.