Preheat your oven to 180ºC and prepare a loaf pan with parchment paper.
Prepare the flax egg: mix 1 tbsp chia seeds with 3 tbsp water and let it sit for 10 mins.
In a medium bowl, combine the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In another bowl, mash the bananas with a fork until smooth. Add the oil and combine well. Then add the flax egg, sugar, vanilla and combine
Pour wet into dry ingredients and mix just until everything is incorporated. Be careful to not over-mix.
Pour the batter into the prepared pan, decorate with chocolate chips (if any) and bake for 55-60 mins or until a toothpick or knife inserted in the middle comes out clean.
Remove from oven and let it cool before slicing. It can last up to 1 week wrapped in cling wrap.