1. In bowl, combine first 9 ingredients, and mix well.
2. Remove 1/3 c.
3. of mixture to small bowl for basting; cover and refrigerate.
4. Pour remaining marinade into large ziplock bag, add tuna.
5. Seal bag, and turn to coat steaks; refrigerate for at least 1 hour.
6. Coat grill rack with nonstick cooking spray.
7. Drain steaks and discard marinade.
8. 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.