Preheat oven to 180 ° C and line a 7" loaf tin with parchment paper.
In a mixing bowl, mash bananas with fork or potato masher.
Add in oil and buttermilk. Stir and add jaggery.
Now add baking soda, baking powder, flour, cocoa powder, and walnuts (save some to use as topping).
Gently mix everything to combine well.
Transfer the batter into a lined loaf tin.
Tap on the kitchen counter to remove air bubbles. Sprinkle some walnuts on top.
Bake in preheated oven for about 35 to 40 minutes or until a skewer inserted into the center of the bread comes out clean.
Remove from the oven and let it cool before slicing.
Notes
I have used plain wheat flour that I use to make roti in this recipe. You may replace it with all-purpose flour if desired.You can also add nuts of your choice.