Preheat your oven to 180 degrees Celsius.
In a large bowl, mash the bananas until they form a smooth. Melt the margarine and stir into the banana with the maple syrup and sugar.
Add the eggs, mix well, then fold in the flour.
Separate half of the mixture into a separate bowl and add the Nutella. Stir well.
Line a loaf tin with baking paper, then spoon in your mixtures. Alternate between the nutella and plain mixture to give the loaf a marble effect.
Bake for 45 minutes, or until a cake tester comes out clean.
Leave to cool, then cut into slices.