For the muffins, preheat oven to 375°F.
Line a 12-cup muffin pan with paper liners (or use a nonstick pan).
Combine flours, baking powder, baking soda, and cinnamon in a medium-sized mixing bowl.
In a separate large bowl, mix together bananas (you can mash them right in the mixing bowl), milk, and Sucanat.
Pour the dry ingredients into the wet mixture and stir until well mixed. Add the walnuts, and spoon the mixture into the muffin cups.
For the topping, mix together Sucanat and cinnamon (and oats, if using) in a small bowl. Combine with a fork until crumbly. Press on top of muffins.
Bake in preheated oven for 18–20 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Cool slightly before serving.