Combine all of the marinade ingredients and whisk vigorously.
Place tuna steaks in a resealable gallon storage bag; add the marinade; toss to coat the tuna steaks.
Refrigerate for at least 30 minutes.
Place marinated tuna steaks on a broiler pan; bake for ~8 minutes on each side, until easily flaked with a fork and center of tuna steak is just barely pink.