Preheat oven to 350 degrees F. Add old fashioned oats, egg, ripe banana, ground flax, vanilla, salt, baking powder, cinnamon, and milk to a medium mixing bowl. Mix with a rubber spatula until combined.
Spray ramkein or baking dish. Pour batter into ramkein. Transfer to the oven to cook for 30-40 minutes, or until top is browned and toothpick comes out clean.