Pop your cashews in a lidded jar. Cover with water. Soak overnight. If you don’t have time to do this, you can skip this step but the smoothie won’t be as smooth.
Drain your soaked cashews. Put them in a blender or food processor. Blitz to a rough paste. Keep the motor going and trickle in 250ml water. Peel the bananas and add them to the blender with the spinach and peeled ginger. Blend till smooth, trickling in more water if needed.