01 - Place Greek yogurt, milk, avocado, banana, spinach (if using), honey or maple syrup, lime or lemon juice, vanilla extract, and ice cubes in blender container.
02 - Blend on high speed until completely smooth and creamy, stopping to scrape down sides as needed.
03 - Taste and adjust sweetness or thickness by adding more honey for sweetness or milk for thinner consistency.
04 - Pour into glasses and serve immediately for best texture and flavor.