Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine frozen hash browns, shredded cheddar cheese, sour cream, and cream of chicken soup.
Stir in chopped onion, melted butter, garlic powder, salt, and pepper.
Mix thoroughly until all ingredients are well combined.
Grease a 9x13 inch baking dish with cooking spray or butter.
Spread the hash brown mixture evenly in the prepared dish.
Bake in the preheated oven for 45 minutes.
Remove from oven and stir to ensure even cooking.
Return to the oven and bake for an additional 15 minutes, or until golden brown on top.
Let cool for a few minutes before serving.