Preheat the oven to 375 degrees. Mix together the frozen hashbrowns, onion, melted butter, cream of chicken, sour cream, and shredded cheddar cheese in a large bowl. Spray down a deep casserole dish with cooking spray. Dump the hashbrown mixture into the pan. Spread evenly in pan with a rubber spatula. Bake in the oven for 45-60 minutes, or until the top is golden brown and the edges start to crisp. Want a loaded hashbrown casserole? Melt slices of Colby jack cheese on top and sprinkle on some bacon. If you want the whole casserole to be loaded, add slices of cheese on top of the casserole during the last 10 minutes of cooking.