Tuna Sauce for Pasta

1 small onion, sliced very finely
2 cloves garlic, whole, in its skin
5 Fresh mint leaves
Olive oil
1/3 cup capers
Tomato concentrate, preferably the thick, dark red Sicilian version
Water from the pasta pot, to thin the sauce
2 cups Tuna, very fresh and cut in 1/2inch cubes
1 glass white wine
1/4 cup soft flavorful black olives, pitted
parsley, chopped finely

Saute the onion, garlic, mint and capers in the oil, making a soffritto. Add tomato concentrate and water and cook a few minutes then add the tuna. Cook the fish just through and then add the white wine and let evaporate. Add the olives and parsley, season to taste, and serve tossed with spaghettini.