1. Preheat the oven to 375°. Slice about ¼ inch off the top of each tomato. Using your index finger or a teaspoon, scoop out all of the pulp and seeds inside the tomatoes, leaving hollow shells about ¼ inch thick.
2. Salt the insides of the tomatoes and turn them upside down over paper towels so that they will drain.
3. Meanwhile, heat the 2 tablespoons of olive oil in a heavy 8-to 10-inch skillet and in it cook the finely chopped onions and garlic over moderate heat, stirring frequently, for 7 or 8 minutes, or until the onions are transparent but not brown.
4. Stir in the fresh white bread crumbs, anchovy fillets and pieces of tuna fish and cook, stirring constantly, for another 1 or 2 minutes.
5. Remove the skillet from the heat and add the finely chopped fresh parsley, capers and olives. If the mixture looks too dry and crumbly, add 1 or 2 more teaspoons of olive oil.
6. Spoon the stuffing mixture into the hollowed tomatoes, sprinkle them with the tablespoon of grated Parmesan cheese and a few drops of olive oil.
7. Arrange the stuffed tomatoes in one layer in a lightly oiled 8- to 9-inch shallow baking dish and bake them on the middle shelf of the oven for 20 to 30 minutes, or until they are tender but not limp and the crumbs on top are brown and crisp.
8. Serve the tomatoes hot or cold, sprinkled with a little chopped parsley. They may be served as part of the antipasto or as a separate vegetable course.
