Add the vanilla Greek yogurt and vanilla extract.

Pour in the frozen blueberries and frozen banana pieces.

Add the rolled oats and freshly grated lemon zest.

Top with the ice cubes.

Blend on low speed for a few seconds, then gradually increase to high speed.

Continue blending until the mixture becomes completely smooth and creamy with no visible oat pieces.

Pause and scrape down the sides if needed to ensure even blending.

Check the consistency and add a splash of milk if a thinner texture is preferred.

Pour into a chilled glass and serve immediately while cold and thick.