Thinly slice the celery (if it’s a large rib, cut in half lengthwise first). Thinly slice the green onions.
Drain and rinse the chickpeas. In a medium bowl, smash the chickpeas with a fork.
Combine the chickpeas with the chopped celery and green onions, mayonnaise, lemon juice, and celery seed. Add about 1/4 to 1/2 teaspoon kosher salt, depending on your chickpea brand and taste preferences, and fresh ground pepper to taste. Taste and salt until the flavor pops! If the salad is dry, add more mayonnaise (cooked chickpeas have a drier texture than canned).
Assemble the chickpea salad sandwich: If desired, spread the bread with hummus (this amps it up a bit but not required). Top the sandwich with lettuce or greens and chickpea spread.