Preheat your oven to 375°F (191°C).
If opting for spinach, ensure it is fully thawed and squeezed dry. If using broccoli, bring a pot of water to a boil, add the florets, and let them simmer for 1-2 minutes until they turn vibrant green.
In a large mixing bowl, combine the cooked chicken, crispy bacon, drained spinach or broccoli, minced garlic, ranch dressing, and half of both shredded cheeses. Stir well to evenly distribute all ingredients. Transfer the mixture into a 9×13-inch (23×33 cm) glass or stoneware casserole dish. You can also mix everything directly in the dish for convenience.
For an extra burst of ranch flavor, consider incorporating 1-3 teaspoons of ranch seasoning mix along with the dressing.
Evenly sprinkle the remaining mozzarella and cheddar cheeses over the top.
Place the dish in the oven and bake for approximately 15 minutes, or until the casserole is heated through and the cheese is melted and bubbly.
Serve warm and enjoy!