In a large bowl, combine 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 tooth pick inserted into the center comes out clean. Let cool slightly before cutting into squares.