In a medium bowl, mash chickpeas with a fork until mostly smooth, leaving some chunks.
Add tahini (or yogurt), Dijon mustard, vinegar, chopped celery, and red onion.
Mix until well combined and season with salt and pepper to taste.
Toast your bread slices if desired, then layer with lettuce, tomato, and generous scoops of the chickpea salad.
Top with the second slice of bread and enjoy immediately.