Preheat the oven to 180°C. Grease and line an approx. 20 cm square baking tin.
Mix together the oats, flour, baking powder, baking soda, cinnamon in a bowl.
In another bowl, combine the oil, eggs and vanilla, the add the mashed banana and kefir/ yogurt. Stir in the maple syrup. Add the oat mixture gradually, stirring carefully until combined.
Transfer the batter into the tin. Bake for 25-30 minutes until golden and cooked through ( test it with a skewer).
Cool for ten minutes in the tin, then transfer it to a wire-rack. Let it cool completely before slicing.
Serve with maple syrup drizzled on top (if you have a sweet tooth).