Preheat the oven to 400 degrees. Place an UNGREASED 10" diameter castiron skillet in the oven while the oven is preheating.
In a medium size bowl combine the white flour and whole wheat flour. Add the baking powder and salt, stirring well.
In a separate bowl, combine the oil, plain yogurt, green onions, dill if using, and black pepper. Blend the yogurt mixture into the flour mixture thoroughly to make a soft dough.
On a floured cutting board, knead the dough about 5 times and pat into a round loaf. Remove castiron skillet from oven and carefully and lightly grease the skillet with butter or oil.
Place the shaped dough into the castiron skillet, spreading and flattening out the dough to fill up the pan almost to the edges. Brush on egg wash or melted butter and bake for about 35-40 minutes or until a knife inserted in the center of the loaf comes out clean.