Preheat Oven at 180 C.Sift all purpose flour, baking powder, baking soda and keep it aside.Peel the skin of bananas and mash it well.Add oil, mashed bananas, vanilla essence in a mixing bowl and mix well. Fold in sugar and mix well until sugar completely dissolves.Now add all purpose flour with baking powder, baking soda slowly to the mix and fold. Do not over mix. The flour must get moistened.Keep 2 tbsp walnuts separately and add remaining chopped walnuts in the mix and give a quick stir.Grease the muffin cups with some oil evenly or use liners and add the batter to it. Make sure to fill each muffin cup till ¾ cup and sprinkle some nuts on top.Bake at same temperature for 25-30 minutes or till it turns golden brown.Once it has cooled down, remove from the muffin cup and enjoy!!