Grease an 8 by 8-inch or 9 by 9-inch square pan with softened butter or nonstick cooking spray. Set aside.
In a large bowl, mix together cornmeal, flour, baking powder, milk, eggs, salt, and oil. Stir in onion and creamed corn. Pour half of batter into prepared pan. Top with cheese and peppers, spreading onto batter. Pour remaining batter on top of cheese and peppers. Bake for about 35 minutes or until golden on top and a toothpick inserted into the center comes out clean. Let cool slightly before cutting into squares.