Preheat oven to 375°F (190°C) and grease a baking dish.
In a large bowl, mix the cooked chicken, diced potatoes, cheddar cheese, sour cream, and milk.
Season with garlic powder, onion powder, salt, and black pepper.
Pour the mixture into the greased baking dish and spread evenly.
Drizzle melted butter over the top and sprinkle with breadcrumbs if desired.
Bake for 40-45 minutes, or until the potatoes are tender and the top is golden brown.
Serve warm and enjoy!