Barbecued Bluefin Tuna

Whisk the orange juice, soy sauce, vinegar, oil, onion, garlic, red pepper flakes, cumin, black pepper, pickling spice, tomato paste and sugar together in a bowl.

Arrange the tuna steaks in a baking dish large enough to hold them in one layer. Pour the marinade over. Marinate, covered and chilled, overnight or up to 24 hours. Drain, reserving the marinade in a bowl.

Grill on a lightly oiled rack set 3 to 4 inches over glowing coals for 3 minutes on each side. Return the tuna steaks to the baking dish. Preheat the oven to 375 degrees F.

Spoon 1 tablespoon of the reserved marinade over each. Bake in the middle of the preheated oven for 4 to 5 minutes or until they are slightly rare. Top each tuna steak with 1 teaspoon of the butter and freshly ground black pepper to taste.