In a small bowl, add oatmeal. Pour milk over top and set aside while preparing the rest of recipe, or leave overnight in the refrigerator.
Preheat oven to 400ºF. Lightly spray a muffin tin with cooking spray.
Cream oil and sugar. Add eggs and continue to beat until light and fluffy.
Add oatmeal mixture and stir to combine.
Combine dry ingredients, then add to wet mixture. Stir until just moistened. Stir in bananas and chocolate chips (if using).
Fill each of the 12 cups in the muffin tin to the top. Bake for 22-25 minutes. Cool.