Preheat the oven to 375 degrees and grease a muffin pan with nonstick cooking spray.
In a large bowl, stir together the bananas, vegetable oil, sugar, eggs, and vanilla.
Add the flour, baking soda, baking powder, and salt. Stir until just combined.
Fill each muffin cup 2/3 full of batter.
Add 1 to 2 teaspoons of Nutella to each cup and use a knife to swirl the spread into the batter.
Bake for 18 to 22 minutes, then allow the muffins to cool in the pan for around five minutes. When they’re safe to touch, transfer the cooked muffins to a cooling rack to cool completely to room temperature.