Cut tomatoes in half, horizontally, remove seeds and inner wateriness.

Process in a bowl the crumbled tuna, the anchovy fillets first washed and pounded to a pulp, and the finely chopped onion and parsley, adding oil as you go to bind and make a fairly soft mixture.

Finally, to this mixture, mix a few tablespoons of mayonnaise, and use it to stuff the tomato halves.