Chop the parsley and mince the garlic.
In medium bowl, mix together the parsley, garlic, orange juice, and lemon juice. Add in the olive oil, soy sauce, oregano, and black pepper. Mix well.
Add tuna to a shallow dish and pour marinade over steaks. Turn to coat one time, refrigerate tuna and marinade for at least 30 minutes.
While tuna is marinading, prepare grill to medium heat. Oil grill grate and cook tuna steaks to desired doneness, about 5 minutes on each side. Brush steaks with marinade between flipping.
Meanwhile, bring remaining marinade to a boil, then remove from heat. Drizzle tuna steaks with reserved heated marinade and serve.