Preheat the oven to 180C/350F. Grease a 6-8 ounce ramekin or oven safe dish.
In a blender, add the oats, banana, apple cider vinegar, milk, peanut butter, baking powder, baking soda, and vanilla, and blend until a smooth batter remains.
Let the batter rest for 5 minutes before transferring it to the greased ramekin. Stir through your mix-ins of choice.
Bake for 12-15 minutes or until the oats puff up and a toothpick comes out mostly clean.
