Place frozen banana, protein powder, Greek yogurt, lemon juice, lemon zest, almond milk, and vanilla extract into a high-speed blender.

Pulse and blend on high speed for 45-60 seconds, using a tamper if necessary to ensure all frozen pieces are processed into a thick, smooth texture.

Adjust consistency by adding additional almond milk one tablespoon at a time if the mixture is too viscous.

Transfer the smoothie mixture immediately into a serving bowl.

Garnish with optional toppings such as granola, fresh berries, or chia seeds and serve while frozen.