Preheat oven to 350 degrees.
Grease a 9x5 inch loaf pan.
In a large bowl, combine flour, baking soda and salt.
In another large bowl, cream together butter and sugars.
Mix in eggs and mashed bananas until well combined.
Add banana mixture into flour mixture and stir until moistened, being careful not to over stir.
Pour ½ of the batter into the loaf pan. Warm Nutella in the microwave for 10-15 seconds or until it softens.
Stir the heated Nutella and pour half of it to the batter in the loaf pan. Use a knife to swirl the Nutella.
Pour the rest of the banana bread batter over the Nutella swirl.
Add the rest of the Nutella to the top of the banana bread batter and use a knife to swirl.
Bake at 350 degrees for 50-55 minutes. If the top starts to get too dark, cover with foil while cooking.