Start by cooking the chicken breasts until tender. You can poach, bake, or grill them as you like. Once cooked, shred the chicken using two forks or your hands.
In a skillet over medium heat, sauté the diced onions and bell peppers until they soften and become fragrant, about 5 minutes.
In a large mixing bowl, combine the shredded chicken, creamed corn, thawed frozen corn, sour cream, sautéed onions and peppers, garlic powder, onion powder, salt, and pepper. Stir everything together until fully incorporated.
Preheat your oven to 375°F (190°C). Spread the creamy chicken and corn mixture evenly into your 9x13-inch baking dish. Top the mixture with shredded cheddar cheese, distributing it evenly.
In a separate bowl, prepare the corn muffin mix according to package instructions, typically by adding water or milk and an egg. Carefully dollop the cornbread batter over the cheesy chicken layer, spreading gently to cover as much surface as possible.
Bake the casserole in the preheated oven for 25-30 minutes or until the cornbread topping is golden brown and cooked through. Once baked, let it cool for a few minutes before serving.
Sprinkle chopped fresh parsley over the top for a fresh pop of color and flavor. Serve warm and enjoy.