Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
In a large mixing bowl, combine shredded chicken, cream of chicken soup, sour cream, French onion soup mix, black pepper, garlic powder, 1 cup mozzarella cheese, and 1 cup French fried onions.
Spread the mixture evenly into the prepared baking dish.
Top with remaining mozzarella cheese and French fried onions.
Bake uncovered for 25–30 minutes, or until hot and bubbly with golden, crispy onions on top.
Serve warm with your favorite side salad or vegetables.