In a large bowl, mash the drained chickpeas with a fork or potato masher until chunky, leaving some whole pieces for texture.
Add the chopped celery, onion, dill, vegan mayo, lemon juice, and salt to the mashed chickpeas.
Mix everything together until well combined. Taste and adjust seasonings as needed.
Either refrigerate the chickpea salad for later use or assemble sandwiches immediately.
To assemble, spread chickpea salad on bread slices and top with lettuce, tomato, sprouts, and mustard as desired.