Preheat oven to 180 degrees Celsius. Line a muffin tray with cupcake liners
Smash bananas with a back of a fork and set aside
Sift the flour and baking powder and set aside
Mix half the walnuts with one tablespoon sugar and one tablespoon butter and set aside
In a large bowl mix together the oil, buttermilk, eggs, sugar and vanilla essence. Mix in the smashed bananas
Add in the sifted flour/baking powder, cinnamon, chocolate chips and half the walnuts. Gently fold it in.
Fill the cupcake liners with equal amounts of the batter
Sprinkle the walnut mixture on top of each muffin
Bake at 180 degrees Celsius for 15-20 minutes or until a toothpick is inserted and comes out clean