Preheat oven to 180°C (350°F) and prepare a muffin mold with muffin liners. Make sure you grease the muffin liners to prevent the desserts from sticking.
In a large mixing bowl, mash three ripe bananas with a fork until completely smooth. Once mashed, add eggs, nut butter, canola oil, vanilla extract and ground cinnamon.
Add coconut sugar and a pinch of salt, then stir the mixture with a whisk or fork until combined.
Stir in the whole-wheat flour and the baking powder, then give it a good mix until smooth. If desired, fold through a handful of chopped walnuts, but do not overmix the batter.
Fill ⅔ of each prepared muffin cup with batter and bake in hot oven for 20 to 30 minutes - mine took 23 minutes. Do not overbake, they are ready when a toothpick inserted into the center comes out clean.
Le cool for at least 15 minutes before serving.