Using a hand mixer cream butter and sugar in a bowl. Add eggs one at a time and mix. In a separate bowl whisk together the flour, baking soda, salt and cinnamon. Add the mashed banana to the creamed sugar and beat until incorporated. Add the dry ingredients and mix until just combined.
Pour half the batter in the loaf pan. Using a spoon pour half the chocolate hazelnut spread down the middle of the loaf pan.
Using a skewer or paring knife, gently swirl the batter and chocolate hazelnut spread together.
Pour the rest of the batter on top and repeat with remaining chocolate hazelnut spread.
Bake for 45-50 minutes until a toothpick inserted into the cake comes out clean.