Add the almond milk. Pour the almond milk into the blender first to help the ingredients blend smoothly.
Add the remaining ingredients. Add the frozen raspberries, Greek yogurt, whey protein powder, and 1 tablespoon of lemon juice.
Blend until creamy. Blend on high for 30 to 60 seconds. Stop and scrape down the sides of the blender if needed.
Adjust the thickness. Add almond milk 1 tablespoon at a time if the smoothie is too thick. Add more frozen raspberries or a few ice cubes if it is too thin.
Taste and adjust. Add the remaining lemon juice for a stronger lemonade flavor. Blend in a small amount of sweetener if the raspberries are especially tart.
Serve immediately. Pour the smoothie into a glass and garnish with fresh raspberries, lemon zest, or a lemon slice.