Prep: Chop banana into 1-inch pieces and freeze for at least 1-2 hours if possible (or overnight).
Process: Add all ingredients to food processor fitted with a standard S blade and process for 2-4 minutes, stopping to scrape the sides down with a plastic spatula as needed (see notes).
Enjoy: Once everything is incorporated and smooth, scoop out mixture into individual bowls. Add any desired toppings, and enjoy immediately.
Notes
Food processor: If you don't have a food processor, you can also use a high-speed blender such as a Vitamix (or even a regular blender) set to medium rather than the highest speed. Because the consistency will be thicker than a regular smoothie, you may need to stop the blender more often and use a plunger or spatula to push everything down towards the blades before continuing to blend.