To make the crumble topping rub the butter into the flour and sugar by rubbing the pads of your thumbs against your fingers in the mixture until it resembles fine bread crumbs.
Stir the oats and seeds into the crumble topping.
Preheat the oven to 375F, butter and flour a 12 hole muffin tin.
In a bowl whisk together the spice, vanilla, banana, sugar and oil until well incorporated.
Add the flour and baking powder and stir in gently with a spatula until just combined, you donâ??t want to overmix the batter.
Divide the batter into the tin, filling each hole â?? of the way, then spoon the crumble topping onto the wet mix.
Bake in the middle of the oven for 18 minutes, until an inserted skewer comes out clean.
Leave to cool in the tin for 15 minutes before removing and allowing to fully cool on a wire rack.