Preheat oven to 350°F (175°C). Line a muffin tin with paper liners.
In a medium bowl, whisk together flour, baking soda, baking powder, and salt. Set aside.
In a large bowl, whisk mashed bananas, granulated sugar, and brown sugar until combined.
Beat in egg, vegetable oil, and vanilla extract.
Gradually stir in dry ingredients until just combined and no lumps remain. Fold in chopped pecans if using.
Fill muffin cups about ¾ full.
Add about 1 teaspoon Nutella to each muffin and use a toothpick to gently swirl into the batter.
Bake for 15–17 minutes, or until a toothpick inserted into the center comes out clean.
Cool slightly before serving your warm Nutella Banana Swirl Muffins.