1. Preheat oven to 350 degrees. Prepare an 8 or 9 inch square baking pan by spraying with non-stick cooking spray.
2. Put rolled oats in food processor or blender and process until oats become a fine meal consistency.
3. Dump powdered oats into a bowl with flour, baking powder, baking soda, and salt, and mix together to combine.
4. In a separate large bowl, put the sugar, applesauce, the whole egg, the egg white, and the vegetable oil, and mix together well until eggs are incorporated.
5. Slowly add dry mixture to wet mixture, stirring with a spoon until mixture is just blended.
6. In a separate bowl, put 1 cup of the batter and add the buttermilk and cocoa, stirring until well mixed.
7. In the large bowl with the remaining batter, stir in the mashed banana and mix well. Spread the mashed banana and batter mixture into the prepared baking pan.
8. Take the cocoa batter and drop by spoonfuls over the banana batter in the baking pan. To form marbling effects, take the tip of a sharp knife, and run it through the two layers of batter, both the spoonfuls of cocoa batter and the banana batter, swirling back and forth in 'S' patterns. Do not over mix.
9. Bake in preheated oven at 350 degrees for 30 to 35 minutes. Check to see if done by inserting wooden pick in center; it should come out dry and clean when done.
10. Remove from oven and cool in pan on rack for 7 to 9 minutes before cutting into bars.