Preheat oven to 350F
Mix the bananas, yogurt, egg, oil, and vanilla together in the bowl until combined.
Add the sugar and continue to mix until combined.
Whisk the flours, flaxseed, baking soda, cinnamon, and salt together in a medium bowl.
Add the dry ingredients to the wet ingredients in the mixer and beat until just combined ( do not over-mix).
Optional stir the nuts into the batter.
Pour batter into a 9 x 5 inch loaf pan coated with cooking spray.
Bake in the oven for 50 to 55 minutes, or until toothpick inserted in the center comes out clean.
Remove from oven and cool for 10 minutes in the pan.
Remove from pan and let cool on wire rack.