Preheat your oven to 350°F (175°C).
In a large bowl, combine frozen hash browns, sour cream, cream of chicken soup, and shredded cheese.
Add chopped onions and season with salt and pepper.
Mix all ingredients until well combined.
Grease a 9x13 inch baking dish with cooking spray.
Spread the hash brown mixture evenly in the baking dish.
Top with additional shredded cheese if desired.
Bake in the preheated oven for 45 minutes or until golden brown.
Let it cool for 5 minutes before serving.
Enjoy your delicious hash brown casserole warm!