Preheat your oven to 375°F (190°C) to ensure that your casserole cooks evenly and achieves that delightful golden finish.
In a large mixing bowl, combine the thawed hashbrowns, shredded chicken, cream of chicken soup, sour cream, ½ cup of the shredded cheddar cheese, diced onion, garlic powder, onion powder, salt, and pepper, mixing everything until well incorporated.
Grease a 9×13-inch baking dish with butter or non-stick spray and pour the mixture into the prepared dish, spreading it evenly.
Drizzle the melted butter over the hashbrown mixture, allowing it to soak into all those wonderful ingredients, and top with the remaining ½ cup of cheddar cheese for that cheesy goodness.
Bake in the preheated oven for 45 minutes or until the casserole is bubbly and golden brown on top, covering it loosely with aluminum foil if you notice it browning too quickly.
Once baked, remove from the oven, allow it to cool for a few minutes, then serve hot.