Add to a blender along with the bananas, vanilla extract, oil, almond milk, vinegar and maple syrup, then blitz until smooth. You could also do this by hand, but a blender gives the best results.
In another bowl, put the remaining ingredients, keeping ½ tbsp oats and 1 tsp sugar to the side.
Pour the smooth banana mixture into the bowl and mix using a large metal spoon.
Divide the mixture between the cases.
Before baking, sprinkle the reserved oats and sugar on the muffins.