Start by cooking the potatoes. Put them in a pot with water and a pinch of salt, bring to a boil and cook for 15-20 minutes, or until they are soft. Drain them and put them in a bowl to cool.
Make the mayo by pureeing the ingredients in a blender or food processor, with enough water to keep it moving. Start with 1/4 cup, and use more if necessary.
Once the potatoes are cooled off, cut them into bite-size cubes and put them in a large bowl.
Add the celery, chickpeas and green onion together in a large bowl, then scoop the mayo over them and toss.
Video
Notes
If you're not using a high-powered blender, you will want to soak the cashews in water for 1-2 hours before making the mayo.