1Place tuna steaks in a large heavy-duty zip-top plastic bag.
2Combine olive oil and next 6 ingredients in a small bowl: stir well.
3Pour marinade mixture over steaks. Seal bag securely; place in a large bowl.
4Marinate in refrigerator for 30 minutes.
5Remove steaks from marinade.
6Spray a grill with cooking spray, and place steaks on grill.
7Cook steaks, covered, over medium coals, basting frequently, for 6 minutes on each side or until fish flakes easily when tested with a fork.