Preheat your oven to 350°F and lightly grease a 9x13 baking dish.
In a large mixing bowl, combine cooked chicken, rice, soup, sour cream, cheese, milk, onion, garlic powder, salt, and pepper.
Mix everything until it looks like it actually belongs together.
Spread the mixture evenly into the prepared dish.
If you want a crunchy topping, toss the breadcrumbs with melted butter and sprinkle over the top.
Bake uncovered for 30–35 minutes until it’s bubbling and the top looks golden.
Let it rest a few minutes before serving (I know, the wait is hard).