In a medium mixing bowl, combine the tuna, celery, Kewpie mayonnaise, shallot, lemon zest, lemon juice, pepperoncini brine, Dijon and capers. Mix until well combined and season to taste with salt and pepper.
Spread the tuna salad onto the bottom half of the bread and top with the pepperoncini peppers. Close each sandwich and cut in half. Serve.
Notes
The salad can be made and stored, refrigerated, for up to three days in advance. Wait to add it to the bread until just before serving so it doesn’t get soggy.