Grind the oat flakes into flour in a blender, add the rest of the base ingredients and blend until you have a sticky dough. Pour this into the slightly greased cake tin (18 cm) and bake for 12 minutes in the oven.
Blend the raspberries, banana juice, coconut milk and maple syrup until smooth.
Boil the berry mixture together with the agar agar in a saucepan for one minute, leave to cool for 10 minutes.
Spread the mixture over the tart base and chill for at least 3 hours.
Decorate with berries just before serving and enjoy!