Preheat the oven to 350 degrees. Spray an 11 x 14-inch baking dish with cooking spray (or lightly grease with olive oil or butter).
In a large bowl combine hash browns, melted butter, cream of chicken soup, sour cream, onion, cheddar cheese, salt, and pepper. Pour into the casserole dish.
Place into the oven and bake for 45 minutes or until the top has browned.