Preheat the oven to 375 degrees F (190 degrees C).

Heat olive oil in a 10-inch cast iron skillet over medium heat; cook onion until soft, about 5 minutes. Stir in ground beef and cook until browned, about 5 minutes more. Drain grease.

Add kidney beans, tomato sauce, corn, chili seasoning, salt, sugars, garlic powder, and Worcestershire sauce. Cook and stir until thoroughly heated, 5 to 10 minutes. Remove from heat and smooth out the top.

Combine cornbread mix, milk, and egg together in a bowl. Mix until a slightly lumpy batter forms. Drop big spoonfuls of the cornbread mixture over the chili; smooth out to the edges of the skillet.

Bake in the preheated oven until top starts to brown, about 15 minutes. Sprinkle Cheddar cheese on top and continue baking until cheese is melted, about 5 minutes more. Let casserole rest for 5 minutes before serving.