The bright acidity of lemon and tangerine juices balances the rich flavor of pesto for a refreshing summery marinade.
Thaw tuna, if frozen. Rinse fish; pat fish dry with paper towels. Place fish in a resealable bag or covered dish; set aside.
For marinade: In a small bowl, combine basil, oil, oregano, thyme, garlic, lemon zest and juice, tangerine zest and juice, kosher salt and pepper. Pour marinade over fish, turning the fish to coat. Chill for 30 to 60 minutes, turning once. Remove fish, reserving marinade. Transfer marinade to a small saucepan. Bring to boiling; reduce heat to low. Simmer, uncovered, for 1 minute.
Place fish on the well-greased rack of a gas or charcoal grill directly over medium heat. Cover and grill fish to desired doneness, gently turning and brushing once with 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 fruity twist on cabbage slaw, try thinly sliced fresh fennel bulb, tangerine segments and fresh mint dressed with a little olive oil, salt, pepper and OJ.