In a 10" cast-iron or other heavy skillet with an oven-proof handle, melt 2 Tbs. butter over medium heat making sure sides and bottom of pan are well coated. Add onions, oregano and if using, jalapeno pepper.
Cook, stirring occasionaly, until onions are a light golden brown, about 10-12 minutes.
Remove 2 tablespoons of onion-mixture, coarsely chop and reserve.
In a large bowl, combine flour, baking powder and salt. Stir in milk, egg, 1/2 cup cheese and onion-mixture from skillet. Stir just until combined.
Pour mixture back into skillet. Top with reserved chopped onion-mixture and remaining cheese.
Sprinkle poppy seeds over the top and bake in a preheated 400-degree oven for 25 minutes. Cool slightly; cut into wedges and serve.