Line a baking tin with muffin wrappers, this recipe yields about 12 baked oatmeal cups.
Preheat the oven to 375°F with a rack in the middle of the oven.
In a large bowl mix together the rolled oats, walnuts, brown sugar, baking powder, cinnamon, salt, and berries. Gently mix in the bananas until they’re evenly distributed. Set aside.
In another medium bowl whisk together the milk, egg, olive oil, and vanilla extract. Pour this mixture over the oat-berries mixture and fold together. Allow to sit 5-10 minutes (important to absorb some of the liquid!) and then mix again.
I like to use a soup ladle to transfer the mixture to the muffin tin, filling each cup about ¾ full. The mixture will still separate a bit just, spoon a good amount of any residual liquid over the oats in each cup.
Bake for 35-45 minutes, or until the oatmeal cups are deeply golden and well set. Remove from the oven and allow to cool a bit on a rack. They’ll continue to set as they cool.