Melt margarine in a large cast iron skillet over medium heat. Add oil.
Pour Bisquick mixture into hot skillet, spoon peaches onto mixture, cover
skillet and cook about 7 minutes.
Remove from stove. Slide cake onto a large plate.
Turn skillet upside down
over the plate, grasping opposite sides of both the plate and skillet with hot
pads, and turn over quickly so that the cake is inverted in the skillet. Cover
and cook the second side about 7 minutes.