Preheat oven to 350 degrees F. Spray a 10- or 12-inch deep skillet (see Notes section below) or sauté pan with nonstick cooking spray.
Combine the Jiffy corn muffin mix, egg, and milk in a medium mixing bowl. Stir until well combined and then add in the frozen corn, stirring until well incorporated. Transfer the cornbread batter to the prepared skillet and set aside.
Combine the chicken, green chiles, red onion, tomato sauce, and BBQ sauce in a medium mixing bowl. Spoon the mixture evenly over the top of the cornbread batter within about ½-inch of the edge (leaving the very outer edge of the cornbread uncovered).
Bake in the preheated oven for 25 to 35 minutes or until the edges of the cornbread are lightly browned. Remove the pan from the oven and sprinkle the cheddar and Jack evenly over the top of the BBQ chicken mixture. Return the pan to the oven for an additional 5 to 10 minutes or until the cheese is melty and glorious.
Remove the pan from the oven, sprinkle with green onions and serve with cilantro, Ranch dressing or sour cream.
Notes
If you use a 10-inch skillet it will yield a thicker, higher profile result and will need to cook a bit longer than if prepared in a 12-inch skillet.