Preheat the oven at 180°C for 10 minutes. Prepare the baking tin by lining with parchment paper and apply oil on surface, coat with little flour.
Sieve the dry ingredients whole wheat flour, baking powder, baking soda, salt, nutmeg powder for 8-9 times. Keep this aside for further use.
In another bowl, mash bananas with a fork. Add jaggery powder and whisk well so that jaggery powder blends well with mashed banana.
Next add oil and milk to mashed banana. Add vinegar to this mixture. Mix well
Add sieved dry ingredients in two batches. Mix one batch of flour into the wet ingredients gently mix with a spatula and next the leftover dry ingredients.
Pour this batter into the prepared baking tin. Now sprinkle the chocolate gratings on top.
Bake in a preheated oven at 180°C for 40 minutes or until the skewer comes out clean.
Whole wheat banana bread is cooled on cooling rack. Serve this warm delicious bread as snack or breakfast with a cup of milk.