Preheat oven to 350°F (175°C).
In a large mixing bowl, combine the cooked chicken, chopped bacon, broccoli florets (or well-drained spinach), and minced garlic.
Add ranch dressing, shredded mozzarella, and cheddar cheese to the mixture. If desired, stir in 1-3 teaspoons ranch seasoning mix for extra flavor. Mix well until all ingredients are evenly coated.
Transfer the mixture to a greased casserole dish and spread evenly.
Sprinkle the topping cheeses (1/2 cup mozzarella and 1/2 cup cheddar) evenly over the casserole.
Bake in the preheated oven for 15-20 minutes until bubbly and cheese is melted and slightly golden.
Remove from oven and let it rest for 5 minutes before serving.