Thaw tuna, if frozen. Rinse fish; pat fish dry with paper towels. Place fish in a resealable plastic bag set in a shallow dish.

For pesto marinade: In a small bowl, stir together basil, oil, oregano, thyme, garlic, lemon peel and juice, tangerine peel and juice, salt and pepper. Pour over fish; seal bag and turn to coat fish. Marinate in the refrigerator for 30 to 60 minutes, turning bag once. Remove fish from marinade, reserving marinade. Transfer marinade to a small saucepan. Bring to boiling; reduce heat. Simmer, uncovered, for 1 minute.

Lightly grease or coat an unheated grill rack with nonstick cooking spray. For a charcoal grill, grill fish on the greased rack of an uncovered grill directly over medium-hot coals until desired doneness, gently turning and brushing once with remaining marinade halfway through grilling. Allow 5 to 6 minutes or until surface is well-marked and the center is still red for medium-rare and 9 to 12 minutes or until fish flakes when tested with a fork and center of fish is still pink for medium doneness. Discard remaining marinade. (For a gas grill, preheat grill. Reduce heat to medium-hot. Place fish on greased rack directly over heat. Cover; grill to desired doneness as above.)

Serve fish with Fennel-Tangerine Salad. Makes 4 servings.

For fennel: Cut off and discard upper stalks of 1 large fennel bulb (about 1 pound). Remove any wilted outer layers and cut a thin slice from the fennel base. Wash fennel and cut in half lengthwise; remove core. Cut into very thin slices (you should have about 2 cups). In a large bowl, toss together fennel slices, 1 cup tangerine sections (from 3 to 4 medium tangerines) or orange sections, 3 tablespoons chopped green onions (green parts only) 2 tablespoons snipped fresh mint, 2 tablespoons tangerine juice or orange juice, 1 tablespoon lemon juice, 1 tablespoon extra-virgin olive oil, 1/2 teaspoon kosher salt and 1/4 teaspoon cracked black pepper. (Salad should not set for more than 10 minutes.)