Heat oven to 350°. Coat a 10-inch cast-iron skillet with nonstick cooking spray.
Place sweet peppers and jalapeño in a microwave-safe dish and microwave 1 minute.
In a large bowl, whisk flour, cornmeal, sugar, baking powder, baking soda and salt. Stir in buttermilk, egg and butter until dry ingredients are just moistened. Fold in peppers and corn.
Spoon batter evenly into prepared skillet. Bake at 350° for 35 minutes. Cool on a wire rack 15 minutes.
Cut into 8 wedges and serve warm or at room temperature.
