Heat oil in large saucepan over medium heat. Add onion, green pepper, and garlic. Cook stirring until translucent, about 5 minutes. Remove 1 cup onion mixture and place in a mixing bowl; set aside. Stir 3 cups water into remaining mixture and bring to a boil.
Meanwhile, add cornmeal to remaining 2 cups of water. In a medium bowl, stir to combine. Add cornmeal mixture to boiling onion mixture. Cook over low heat, stirring constantly until cornmeal is thickened, 4-6 minutes.
Coat 9x13 baking dish with cooking spray, Spread cornmeal mixture evenly over bottom of dish.
Combine beans, corn, and chicken with reserved onion mixture.
Spread 1 can of enchilada sauce over cornmeal, cover with bean mixture. Pour 2nd can of enchilada sauce over top. Cover with cheese. Bake for 45 minutes.