Preheat the oven to 200C and prepare a muffin tin with liners.
Prepare the streusel topping first by stirring the oats with brown sugar, cinnamon and almonds.
Then rub the cold butter into the mixture to create a coarse mixture.
Then in a mixing bowl whisk the butter and sugar together until light and fluffy.
Add the banana puree and whisk. Add the egg and vanilla and beat for few more minutes.
Then add the dry ingredients.
Scoop the batter out into each cupcake liner, up to ¾th level.
Sprinkle some of the streusel mixtures on top of each cupcake.
Bake for 20 minutes.
Remove and let cool completely before serving.