Slice the tuna thin, but not too thin. Shoot for about 1/4 inch thick. A tip on cutting cleanly: Draw your (very sharp) knife back towards you to cut, so you only slice in one direction. Sawing through fish makes it raggedy.
Arrange the fish on a plate or plates, and distribute the oil, lemon juice, capers, salt and lemon zest around it. Serve immediately,
A very dry white wine or dry rose are good choices here. This isn't really beer food, but a crisp pilsner would work.