Preheat Oven: Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish.

Mix Ingredients: In a large mixing bowl, combine the shredded chicken, thawed hash browns, cream of chicken soup, sour cream, shredded cheddar cheese, melted butter, chopped onion, peas and carrots, garlic powder, onion powder, paprika, salt, and pepper. Mix until well combined.

Transfer to Baking Dish: Spread the mixture evenly in the prepared baking dish.

Optional Topping: If using, combine the crushed cornflakes or breadcrumbs with the melted butter in a small bowl. Sprinkle the topping evenly over the casserole.

Bake: Bake in the preheated oven for 45-50 minutes, or until the casserole is bubbly and the top is golden brown.

Serve: Remove from the oven and let it cool slightly before serving. Enjoy your comforting and hearty Hashbrown Chicken Casserole!