Preheat oven to 350℉ and line a muffin pan with paper liners.
In a large bowl, combine the oat flour and baking soda. Set aside.
In another medium bowl, combine the mashed bananas and berries. Add in the oil, milk, and beaten egg. Then carefully stir in the peanut butter and mix until the mixture is smooth and creamy.
Pour the wet mixture into the large bowl of flour. With a spatula, stir the ingredients together until a batter forms. It will appear slightly loose.
Fill the cupcakes lines ½-¾ of the way full with the batter.
Bake for 15 minutes or until the center comes out clean with a toothpick. Let cool for 10 minutes before frosting.
