Wash spinach, if needed, under cold running water and remove excess moisture with paper towels. Peal the banana and orange.
In a blender, add the the juice of ½ lemon, spinach, orange, banana, and water (for a slightly runnier texture). Make sure no lemon seeds fall into the blender.cup!
Cover the blender with the lid and blend on high speed until all the ingredients are well combined. Adjust the amount of water, if needed, to achieve the desired thickness.
Pour the smoothie into a glass and serve immediately.