If using canned white beans, drain and rinse them, then place them into a large bowl. If you're using dried white beans that have been soaked overnight, cook them as per the packages instructions and let them cool.
Drain the mackerel, and add the mackerel to the bowl with the white beans followed by the celery, carrots, scallions, mayo, lemon zest, lemon juice, dill, and salt; add cracked black pepper to taste.
With a fork, mix the ingredients well, roughly smashing the white beans and flaking the mackerel in the process.
Once fully mixed, spoon the mixture onto toast, into a wrap, or into a lettuce cup.
Optional: Top with thinly sliced radishes, cucumbers, fresh dill, and fresh chives. Serve with fresh lemon wedges.