Add the old-fashioned rolled oats, banana, greek yogurt, milk, peanut butter (or almond butter), maple syrup, and ground cinnamon to a high-speed blender like Vitamix Blender.
Blend until smooth and creamy. If it's too thick, add more milk as per your preference.
Pour into glasses and garnish with sliced banana, rolled oats, and a sprinkle of ground cinnamon on the top if desired. Serve immediately and enjoy!