Preheat oven to 375 degrees F.
In a medium bowl, combine flour, oats, white sugar, brown sugar, baking powder, baking soda and salt. Stir until ingredients are well combined.
In a large bowl, beat egg. Add milk, oil, vanilla and mashed bananas. Sir to mix ingredients until well combined. Add flour mixture to the banana mixture and stir until ingredients are incorporated, do no over stir.
Line a 12 muffin pan with 12 muffin tins or spray muffin tin generously with cooking spray. Divide batter evenly among the 12 muffin tins.
Add a teaspoon of Nutella to the top of each muffin and gently cut Nutella into batter with a knife or toothpick to produce pretty swirls. I also added a small amount of batter on top of the Nutella to make the swirling process easier.
Bake your Nutella Banana bread muffins at 375 degrees for 15-18 minutes or until golden brown and a tooth pick inserted in the middle comes out clean.
Enjoy your muffins warm or stored in an airtight container for up to a week.