Preheat the oven at 175 C / 350 F. Line an 8" loaf pan with parchment paper.
Add the dry ingredients (buckwheat flour, baking powder, salt, cinnamon, coconut sugar) into a mixing bowl EXCEPT for the walnuts. Give them a mix.
In another bowl, add the bananas and mash them with a fork.
Add the wet ingredients (peanut butter, vanilla extract, kombucha) to the banana. Mix to combine.
Add the wet mixture to the dry one. Stir to combine all.
Stir in half the amount of the walnuts. Pour the mixture into the lined pan(s). Sprinkle the left walnuts on top.
Bake at 175 C / 350 F for 35-40 minutes until a toothpick inserted in the center comes out clean. Let it cool for 20 minutes before removing from the pan. Slice (and spread some peanut butter on it if you will) and EAT!