Gather all your ingredients together including the cooked chicken, bacon, garlic, ranch dressing, cheeses, broccoli, and spinach.
In a large skillet over medium heat, cook the bacon until crispy, then chop into bite-sized pieces.
In the same skillet, sauté the minced garlic for about 1 minute until fragrant.
In a large mixing bowl, combine the cooked chicken, chopped bacon, sautéed garlic, ranch dressing, half of both shredded cheeses, broccoli florets, and well-drained spinach. Mix until evenly coated.
Preheat your oven to 350°F (175°C). Transfer the chicken mixture into a greased baking dish and spread it out evenly.
Sprinkle the remaining mozzarella and cheddar cheese on top of the casserole mixture.
Bake for about 15 minutes or until the cheese is bubbly and golden brown.