Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish or casserole pan.
In a large mixing bowl, combine the cooked chicken, cooked rice, broccoli, cream of chicken soup, sour cream, milk, garlic powder, onion powder, salt, and pepper. Stir in 1 cup of the shredded cheddar cheese until everything is well mixed.
Pour the mixture into the prepared baking dish and spread evenly with a spatula.
Sprinkle the remaining ½ cup of shredded cheddar cheese over the top. Add Parmesan cheese or crushed crackers if using for extra texture and flavor.
Bake uncovered for 30–35 minutes, or until the casserole is hot and bubbly and the cheese is melted and lightly golden.
Let rest for 5 minutes before serving to allow it to set slightly. Serve warm and enjoy!