Prepare the chickpeas: drain and rinse the canned chickpeas well, then pat them dry with paper towels. Drying removes excess liquid so the salad isn’t watery and helps the dressing cling to the chickpeas.

Roughly mash the chickpeas in a medium bowl: use a potato masher or the back of a fork to mash about 50–70% of the chickpeas, leaving some whole for texture. Mashing releases starches that help bind the mixture while keeping bite and variety of texture — aim for a mix of creamy and pea-like whole beans.

Build the dressing: in a small bowl whisk together the Greek yogurt, Dijon mustard, lemon juice, lemon zest (if using), olive oil, salt and pepper. Whisking emulsifies the oil into the yogurt and mustard so the dressing is smooth and coats the chickpeas evenly.

Combine salad components: to the mashed chickpeas add the diced celery, chopped dill and optional sliced red onion. Pour the dressing over and fold gently until combined. Folding (not over-stirring) keeps some chickpeas intact and prevents the mixture from becoming gluey.

Taste and adjust: taste the salad and add more salt, pepper or lemon juice as needed — brightness is key here because it lifts the neutral chickpea base. If you prefer it creamier, stir in up to 1 more tablespoon yogurt (or mayo if using).

Toast the bread: toast the whole-grain slices until golden and slightly crisp. Toasting creates a barrier that prevents sogginess and adds nutty, caramelized flavor and a satisfying crunch to each bite.

Assemble the sandwiches: divide the chickpea salad into two equal portions. On two slices of toasted bread, lay a lettuce leaf (this also acts as a moisture barrier), heap the chickpea salad, sprinkle a pinch of paprika if using, and top with the second slice of bread. Building with lettuce first keeps the toasted bread crisp and adds fresh crunch.

Serve and enjoy immediately, or wrap tightly for transport and refrigerate for up to 24 hours. If making ahead, keep lettuce separate and add just before eating to maintain crispness.