Preheat the oven to 350°F (175°C).
In a large bowl, mix the cream of chicken soup, sour cream, milk, garlic powder, salt, and pepper.
Stir in the cooked chicken, rice, broccoli, and 1 cup of shredded cheddar cheese.
Transfer the mixture into a greased 9x13-inch baking dish and spread it evenly.
Top with the remaining cheddar cheese.
If using the cracker topping, mix the crushed crackers with melted butter and sprinkle over the top.
Bake uncovered for 25–30 minutes, or until bubbly and golden on top.
Let rest for 5 minutes before serving.