Preheat oven to 375 degrees F. Grease or spray 10 muffin cups, or line with muffin papers.
In a large bowl, combine flours, baking soda, baking powder and salt. In a smaller bowl, beat together bananas, sugar, egg and oil. Add the banana mixture to the dry ingredients and mix until just moistened. Spoon batter into prepared muffin cups.
Spoon a dollop of Nutella onto each muffin and swirl together well.
Bake in preheated oven for 15-17 minutes, until a toothpick inserted into center of a muffin comes out clean.