Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, cream of chicken soup, sour cream, garlic powder, salt, and pepper.
Stir in the mixed vegetables and cooked rice or pasta until evenly combined.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it out evenly.
Sprinkle the shredded cheddar cheese generously over the top.
Cover the dish with aluminum foil and bake for 25 minutes.
After 25 minutes, remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden brown.
Allow the casserole to cool for a few minutes before serving.