Pour 1/2 cup marinade into a large ziplock baggie and add tuna.
Seal bag and be sure tuna is fully coated in marinade.
Refrigerate for 2 hours. (Careful not to over-marinate the fish- the acidity will cook it if marinated too long!).
Cover and refrigerate remaining marinade.
Coat grill rack with nonstick cooking spray before starting grill. Grill drained tuna, uncovered, for 2-4 minutes per side. (We like our's pink/rare on the inside) If you prefer yours to be flaky, grill for 5-7 minutes per side.