Line a 12-hole muffin tin with paper muffin cases.
Sift the flours and baking powder into a large bowl, then stir in the oats. In a separate bowl, whisk together the oil, eggs, milk and sugar, then pour into the dry ingredients and mix together until just combined – do not over-mix.
Gently stir in the bananas and stem ginger, then spoon the mixture into the paper cases. Bake in a preheated oven, 200˚C (400˚F), Gas Mark 6, for 20 minutes.
Remove the muffins from the tin, then pour over the ginger syrup and leave to cool on a wire rack.