Pour the almond milk or water into a high-speed blender base.
Add the banana, protein powder, rolled oats, and crushed walnuts.
Incorporate the ground cinnamon, ground nutmeg, and vanilla extract.
Add ice cubes to the blender.
Secure the lid and blend on high speed for 45 to 60 seconds until the texture is completely smooth and homogeneous.
Pour into a glass and consume immediately for optimal nutrient absorption.