Preheat oven to 375°F (190°C).
In a large mixing bowl, combine shredded chicken, cooked rice, broccoli, cream of chicken soup, sour cream, milk, garlic powder, salt, and black pepper.
Stir until well mixed.
Transfer the mixture to a greased 9x13-inch baking dish.
Sprinkle shredded cheddar cheese evenly over the top.
If desired, add breadcrumbs for a crispy topping.
Bake for 25-30 minutes or until hot and bubbly.
Let cool for a few minutes before serving.