Preheat oven to 170° C / 340° F.
Put approx. 400 g. of peeled bananas, the maple syrup, almond butter and lemon juice in a mixer bowl and blend until there are no large pieces of banana. If you do not have a mixer you can press the banana with a fork and add the other ingredients and mix with a spatula.
Transfer the banana mixture to a large bowl. Sieve the flour and add the baking powder and cinnamon and mix. Start adding the dry ingredients into the wet mixture in batches. Mix continuously with a spatula until flour is fully incorporated. If you want to use some nuts add the nuts to the batter.
Lay a baking paper in a bread baking tin. If you do not want to use baking paper , then you should brush the tin with few drops of oil. Transfer the batter into the baking tin.
Bake for about 55-60 minutes, or until a toothpick comes out fairly.
Remove the banana bread from the oven. Allow it to cool down completely. Otherwise it might taste a bit raw if you try to eat it warm.