Preheat your oven to 350 degrees F.Spray an 8x8 square pan with cooking spray.In a large bowl or stand mixer, mix together all the dry ingredients (oat flour, whey protein, baking powder, salt, stevia).Add in the canned pumpkin, milk, egg and egg whites. Mix until fully combined.Meanwhile, mix together the topping ingredients in a small bowl.Pour half the pumpkin batter into your baking pan. Smooth it out. Sprinkle half of the cinnamon/stevia mixture on the batter.Pour the remaining batter in the pan, smooth it out, and sprinkle the remaining cinnamon/stevia mixture on the top.Take a knife and swirl the batter to create a marbled look.Bake for 20-22 minutes until just cooked but still moist.