Preheat the oven to 350°F and lightly grease an 8x8 baking dish.
In a large mixing bowl, combine the cooked rice, diced chicken, broccoli florets, cream of chicken soup, milk, garlic powder, salt, and pepper.
Stir in 1 cup of the shredded cheddar cheese until everything is evenly coated.
Transfer the mixture to the prepared baking dish and spread it into an even layer.
Sprinkle the remaining 1/2 cup of cheddar cheese over the top.
Bake for 25 to 30 minutes until the cheese is melted and the casserole is bubbling around the edges.