Use a small food processor to pulse up the chickpeas a few times, then add them to a medium bowl. Or smash them by hand in the bowl with a fork.
To the chickpeas, add mayo, vinegar, salt and pepper and mix thoroughly. Stir in onion and celery. Taste, adjust salt and pepper to your liking or add another splash of rice vinegar for more tang.
Lightly toast your bread, if desired. Divide chickpea tuna between 4 slices of bread. Top with another slice, or serve open-faced for smaller appetites.
Chickpea tuna keeps really well for 3-4 days, in a resealable container in the fridge for 3-4 days.I recommend erring on the side of using slightly less mayo for longer storage, and adding a bit more before serving to freshen up the texture.