Preheat your oven to 350°F (175°C).
In a large bowl, combine thawed hash browns, sour cream, cream of chicken soup, and melted butter.
Add chopped onion, salt, and pepper to the mixture.
Mix in 1.5 cups of shredded cheddar cheese.
Transfer the mixture to a greased 9x13 inch baking dish.
Spread it evenly across the dish.
Top with the remaining 0.5 cup of shredded cheddar cheese.
Bake in the preheated oven for 45 minutes or until the top is golden brown.
Let it cool for 5-10 minutes before serving.
Garnish with chopped green onions if desired.