We tend to have tuna sandwiches with sweetcorn or cucumber in the UK. I like the American style tuna salad sandwich, which is mixed with mayonnaise and a pickle such as finely sliced cocktail gherkins. It's simple, quick and rather addictive. Usually I'd say buy a good Spanish or Portuguese brand of tuna but the mayonnaise makes even the cheapest tuna taste good.You can swap out the gherkins for silver skin onions, or pickled green peppercorns or capers. You can build in a crisp lettuce leaf to the sandwich or slices of cucumber to add crunch.