Preheat oven to 180C (fan) and line a 12 hole silicon muffin / fairy cake tin with paper cases.
In a bowl sift the flour, bicarbonate of soda and salt.
In a larger mixing bowl mix together oil, sugar, eggs, mashed bananas, vanilla extract and peanut butter until the mixture is thick.
Add the flour mixture from the first bowl to the banana mixture and gradually fold all of the ingredients together.
Spoon a little of the muffin mixture between the 12 paper cases. Just enough to cover the base of each of the cases.
Add ½ tsp. peanut butter filling into the centre of the mixture in each of the 12 paper cases.
Add the rest of the muffin mixture into each paper case.
Bake for 15 – 20 minutes in the centre of an oven until risen and brown. Check the centre of one with a tooth pick to ensure it comes out clean.
Transfer and cool on a wire rack.