Preheat oven to 350. Prepare a 2-quart casserole dish with cooking spray; set aside. Meanwhile, in a large skillet, cook chicken and onions until chicken is no longer pink. Add salt, black pepper and corn. Mix well. Pour into prepared dish. Arrange tater tots on top. In a small bowl, combine soup and water. Pour mixture over top tater tots in dish. Bake, uncovered, for 45 minutes.