Mash the oil-packed tuna with mayonnaise, chopped celery, capers, gherkins, lemon juice, salt, white pepper, and chives.
Let the salad chill for a few hours to meld the flavors.
Toast the English muffin or bread and spread both sides with a thin layer of mayonnaise.
Add a leaf of lettuce for crunch.
Pile on the tuna salad, then top with sliced tomato and onion.
If using bread, close it up with a second slice; if using an English muffin, leave it open-face.
