Preheat the oven to 200°C, gas mark 6. Line a 12 hole muffin tin with muffin cases. Sift the flour into a large bowl and mix in the oats and sugar.
In a separate bowl mash the banana and mix in the peanut butter, eggs, butter and milk. Stir into the flour mixture. Spoon into the muffin cases and bake for 20 minutes or until golden.