Preheat the oven to 375°F (190°C) and lightly grease a 9x13-inch baking dish.
In a large bowl, mix together cooked chicken, cream of chicken soup, sour cream, frozen vegetables, garlic powder, onion powder, salt, and pepper. Stir in 1 cup of shredded cheddar cheese.
Spread the chicken mixture evenly in the baking dish.
Top with mashed potatoes, spreading smoothly to cover the filling. Sprinkle the remaining 1/2 cup cheese on top.
Bake uncovered for 25–30 minutes, until heated through and bubbly. If desired, add crispy fried onions on top during the last 5 minutes of baking.
Let cool slightly before serving warm.
Prep Time: 15 minutes | Cook Time: 30 minutes | Total Time: 45 minutes
Kcal: Approx. 410 per serving | Servings: 6