Heat oven to 350F. If your doughnut pan is nonstick (I think most are) then do not spray. Otherwise, if it isn't nonstick, spray with cooking spray and set aside.
In a large mixing bowl, combine the flour, whole wheat flour, baking soda, baking powder, salt and cinnamon until well combined.
In a second bowl, stir together the egg, sugar, bananas and oil until well combined. Add to dry ingredients and stir until just combined.
Spoon some of the batter into each of the doughnut pans with a spoon. Alternately, you can spoon the batter into a pastry bag and pipe the batter into the pans, if desired.
Bake 10 to 14 minutes or until toothpick inserted into doughnuts comes out nearly clean with just a few moist crumbs. Cool 10 minutes in pan. Remove from pan and cool completely on wire cooling rack.
Meanwhile, stir together the milk and powdered sugar. Spoon glaze over warm doughnuts. Dust with powdered sugar, if desired.
Recipe by Espresso and Cream at https://www.espressoandcream.com/2015/02/baked-banana-bread-doughnuts.html