Drain the tuna and place in a bowl. Cut a little with a fork. Add salt, pepper and balsamic vinegar. I usually use more balsamic vinegar because the tuna soaks up a lot. Wash the lettuce, shred it and add it to the bowl. Finely chop some garlic leaves, alternatively chives or a small onion and add them as well. Finally pour the oil over it and mix everything together.
A low-carb (evening) meal without bread. Otherwise, baguette tastes good with it.