1. If the fish is frozen, thaw it first. Rinse the fish and pat it dry with paper towels. Set it aside.
2. In a small bowl, combine 1 teaspoon of vinegar, olive oil, Italian seasoning, salt, and 1/4 teaspoon of pepper. Brush this mixture on both sides of the tuna steaks. Set the tuna aside.
3. In a medium bowl, stir together tomatoes, fennel, basil, shallot, garlic, the remaining 2 teaspoons of vinegar, and the remaining 1/4 teaspoon of pepper to make the tomato salad. Set it aside.
4. If using a charcoal grill, place the fish on a greased grill rack directly over medium coals. Optionally, you can cover the grill grate with foil before putting the fish on. Grill the fish, uncovered, for 6 to 8 minutes or until it starts to flake when tested with a fork, flipping it once during grilling.
(If using a gas grill, preheat it and then reduce the heat to medium. Place the fish on a greased grill rack over the heat. Cover and grill as directed.)
5. Serve the tuna with the reserved tomato salad. Sprinkle with pine nuts and Parmesan.
6. Toast the pine nuts in a dry skillet over medium heat, shaking the skillet frequently to prevent burning.