Preheat oven to 450°.
Coat a nonstick skillet with cooking spray; place over medium-high heat until hot. Add onion, and saute until tender.
Add soup and corn to skillet, stirring well; spoon mixture into an 8-inch square baking dish coated with cooking spray. Sprinkle cheese over soup mixture.
Combine cornbread mix and water, stirring just until smooth. Pour batter over mixture in baking dish; bake at 450° for 18 minutes or until golden.