Preheat the oven to 400°F (200°C).
In a skillet, heat olive oil over medium heat. Add diced onion and bell peppers. Sauté for about 5 minutes until soft.
In a large mixing bowl, combine the cooked chicken, sautéed vegetables, corn, and 1/2 cup of shredded cheddar cheese. Mix well.
In another bowl, prepare the cornbread batter by combining the cornbread mix, milk, eggs, garlic powder, salt, and black pepper. Whisk until smooth.
Spread the chicken and vegetable mixture evenly in the casserole dish. Pour the cornbread batter over the top, spreading it gently to cover the chicken mixture.
Sprinkle the remaining 1/2 cup of shredded cheddar cheese on top of the cornbread batter.
Bake in the preheated oven for 30-35 minutes, or until the cornbread is golden brown and a toothpick inserted into the center comes out clean.
Let it cool for a few minutes before serving. Cut into squares and enjoy!