To prepare the tuna, gather the ingredients: 1/4 cup of orange juice, 1/4 cup of soy sauce, 2 tablespoons of olive oil and 1 tablespoon of lemon juice. Also gather 2 tablespoons of chopped parsley, a clove of minced garlic, 1/2 teaspoon of oregano, 1/2 teaspoon of black pepper and 4 tuna steaks that weigh roughly 4 ounces each.
In a large mixing dish, combine the orange juice, soy sauce, olive oil and lemon juice. Toss in the parsley, garlic, pepper and oregano, and mix well. When the mixture is ready, place the tuna steaks inside the marinade, and turn the steaks over to coat them well. Try to cover as much of the steaks as possible, and when ready, cover the marinade, and allow the steaks to refrigerate for a minimum of half an hour.
When the marinated steaks are ready for cooking, preheat the grill for a high heat setting. Lightly oil the grill's grate, and cook the tuna steaks. Cook the steaks on one side for about six minutes, then turn them over, and baste with marinade. Discard the remaining marinade, and cook the steaks for an additional six minutes, or until they reach the desired doneness.