Preheat oven to 350 degrees F. Heat a 12-inch oven proof skillet over medium and melt butter with brown sugar. Add bananas and saute until sugar becomes a syrup and remove from heat. Arrange bananas neatly in pan and set aside.
In a large bowl, mix flour, cocoa powder, baking powder, baking soda, cinnamon and chocolate chips. In another bowl, combine egg whites, brown sugar, yogurt and vanilla. Add dry ingredients to wet ingredients and mix until just combined. Pour into skillet over sauteed bananas. Bake for 20-25 minutes, or until middle of cake springs back when touched.
Remove from oven and cool slightly. Invert onto a large plate and cut into 16 slices.