In a large bowl, stir together cooked rice, cream of chicken soup, sour cream, whole milk, shredded cheddar, garlic powder, and black pepper until well combined. Fold in the broccoli and mix evenly. Spread the mixture into the prepared baking dish.
4 cups cooked white rice, 1 can cream of chicken soup, 1/2 cup sour cream, 3/4 cup whole milk, 2 & 1/2 cups shredded cheddar cheese, 1 teaspoon garlic powder, ½ teaspoon black pepper