1/4 cup reduced-sodium soy sauce
3 tablespoons brown sugar
3 tablespoons olive or canola oil
2 tablespoons white wine vinegar or cider vinegar
2 tablespoons sherry or chicken broth
2 tablespoons unsweetened pineapple juice
2 garlic cloves, minced
1 1/2 teaspoons ground ginger
4 (6 ounce) tuna steaks
In a bowl, combine the first eight ingredients; mix well. Remove 1/3 cup to a small bowl for basting; cover and refrigerate. Pour remaining marinade into a large resealable plastic bag; add tuna. Seal bag and turn to coat; refrigerate for up to 1 hour.
Coat grill rack with nonstick cooking spray before starting the grill. Drain and discard marinade. Grill tuna, uncovered, over medium heat for 5-6 minutes on each side or until fish flakes easily with a fork, basting frequently with reserved marinade.