Prep your liquid base: If using coffee or green tea, chill it first. Combine with milk to total about 3/4 to 1 cup liquid, depending on how thick you like it.
Add the dry ingredients first: Put rolled oats, flax or chia, and cinnamon into the blender.
Blending them early helps create a smoother texture.
Add the creamy elements: Drop in banana, Greek yogurt, nut butter, and vanilla.
Pour in the liquids: Add your milk (and coffee or green tea if using).
Blend until smooth: Start low, then increase to high for 30–45 seconds until silky. Scrape the sides if needed.
Adjust: For thickness, add more ice or a few extra oats. For a thinner sip, splash in more milk.
Taste and add a touch of sweetener if desired.
Serve right away: Pour into a cold glass or to-go bottle. Sprinkle a pinch of cinnamon on top if you like.