In a high-speed blender, add the old-fashioned rolled oats, large egg, over-ripe banana, nut butter, almond milk, vanilla extract, baking powder, and ground cinnamon. Blend on medium speed for 20-40 seconds until smooth and creamy.

Transfer the blended mixture into a mixing bowl, and gently fold in your choice of mix-ins, such as chocolate chips or blueberries.

Grease a microwave-safe ramekin or large mug thoroughly with cooking spray. Pour the batter into the prepared ramekin, filling it no more than halfway.

Place the ramekin in the microwave and cook on high for 90 seconds, checking for doneness. Continue cooking in 10-second increments if needed.

Once cooked, carefully remove the ramekin from the microwave and allow it to cool for a minute. Serve warm with toppings like extra nut butter or fresh fruit.