Preheat oven to 170°C. Line 12 muffin tins with cupcake papers.
Sift together flour, baking powder, baking soda, and cinnamon; set aside.
In a large bowl, combine the bananas, brown sugar, egg, and melted butter.
Stir in the flour mixture, and mix until smooth. Scoop into muffin pans.
Add a generous dab of Nutella to the top of each muffin and swirl the top using a toothpick.
Bake the muffins for 20 to 25 minutes until lightly golden