You need:
8 big tomatoes

plus for the sauce:
1 can tuna fish (200 g)
1 onion
4 anchovies filets (anchoga)
3 tb mayonnaise
1 yogurt (180 g) (if possible the one from buffalo milk)
a bit grated lemon peel

plus for the garnish:

1 can tuna fish (200 g)
Lemon slices

Open the tuna cans and drain the water/oil.

Cut the onion in pieces, and fill together with one of the drained tuna cans, anchovies, mayonnaise, yogurt and lemon peel in a blender, and blend to a creamy paste. Season with salt and pepper.

Cut the tomatoes in very thin slices, arrange as a circle on a plate and put the sauce in the middle.
Decorate with the tuna from the second can, capers and lemon slices.