In a medium sized bowl, mash the chickpeas with a fork. You can also use a food processor, if you prefer. A little bit of chunkiness is fine. You're going for a mashed chickpea texture, not a totally smooth, hummus situation.
Add the mayo, celery, onion, and sunflower seeds. Stir to combine them will with the mashed chickpeas.
Gently fold in the grapes until they're evenly incorporated. Season to taste with salt and pepper.
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Notes
If you don't want to use canned chickpeas, you can use 1 ½ cups of cooked chickpeas instead.This salad will keep for 3-5 days in the refrigerator.