Preheat the oven to 350 degrees F (180 degrees C) and grease and line a large loaf pan.
Peel the bananas and add them to a large mixing bowl. Mash them thoroughly with a fork.
Add all remaining ingredients except for the chopped walnuts to the bowl. Mix with an electric hand whisk until just combined.
Transfer the mixture to your lined loaf tin and sprinkle over the chopped walnuts. Bake for 50 minutes to 1 hour, or until a skewer inserted into the center of the loaf comes out clean or with just a few moist crumbs.
Leave the banana bread in the tin for about 10 minutes before transferring to a wire rack to cool. Allow loaf to cool for about 1 hour before slicing.