In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in chili and water. Bring to a boil. Reduce heat; cover and simmer for 10 minutes. Pour into two 2-cup baking dishes.
In a small bowl, combine the cornbread mix, milk and egg. Stir in cheese and corn just until combined. Spread batter evenly over chili.
Bake at 400° for 15-18 minutes or until topping is golden brown.