Preheat oven to 350°F. Line muffin pans with 13 paper or silicone liners. *SEE NOTE*
In a large bowl, mash the bananas, then whisk in the sugars and egg until combined. Whisk in the butter and vanilla extract.
Sprinkle the flour, baking soda, baking powder, and salt on top, giving the powders dry ingredients a quick whisk before gently stirring them into the banana mixture until no white streaks remain.
Use an ice cream scoop or spoon to scoop the batter into each muffin liner, filling it about 2/3 of the way full.
Warm the nutella in the microwave for about 15 seconds to make it easier to swirl. Add a dollop of chocolate spread over each muffin batter. Use a toothpick to swirl into the batter.
Bake muffins for 19-23 minutes, or until a toothpick inserted in the center comes out clean.
Remove to a wire rack and serve warm or cool completely before storing. Muffins can be stored in an airtight container with paper towels on the bottom and top of the muffins.