Prep your blender. Add the milk first.
Liquids at the bottom help the blades catch everything and create a smoother blend.
Add the dry ingredients. Sprinkle in the oats and cinnamon so they blend down into a fine, muffin-like texture. The oats thicken as they blend.
Layer the creamy elements. Add Greek yogurt, almond butter, vanilla, and a pinch of salt. These build body and flavor.
Finish with the fruit. Add frozen blueberries and the frozen banana on top.
If using lemon zest, add it now.
Blend until smooth. Start on low, then move to high for 30–45 seconds. Scrape the sides if needed and blend again until velvety.
Taste and adjust. If you want it sweeter, add maple syrup or honey. For a thicker smoothie, add a few ice cubes and blend again.
Serve immediately. Pour into a chilled glass.
Top with a sprinkle of oats or a few extra blueberries if you like a little texture on top.