These oatmeal cups can be frozen for up to a month!
In a large bowl, mash banana with a fork or potato masher. Add eggs and stir into bananas until combined. Add rest of ingredients, except blueberries and walnuts. Mix well.
Fold in blueberries and nuts stirring gently. Using a large size ice cream scoop, portion mixture into a greased muffin tin.
Bake at 425 F for 15 minutes. Leave to cool in muffin tin for 10 minutes to set up, then remove from tins and place in cupcake liners to cool completely.