Place the chickpeas in a mixing bowl and mash with a fork, leaving only a few beans whole.
Add tahini, mustard, maple syrup, red onion, celery, pickle, capers, salt and pepper, and sunflower seeds (if using) to mixing bowl. Mix to incorporate. Taste and adjust seasonings as needed.
Toast bread if desired, and prepare any other desired sandwich toppings (such as lettuce, tomato, and onion).
Scoop a healthy amount of the chickpea mixture onto one slice of bread, add desired toppings and top with second slice of bread. Repeat for additional sandwiches.