Gather all ingredients.

Mix orange juice, soy sauce, olive oil, parsley, lemon juice, garlic, oregano, and pepper together in a large non-reactive dish until well combined. Place tuna steaks in marinade and turn to coat. Cover the dish with plastic wrap and marinate in the refrigerator for at least 30 minutes.

Preheat an outdoor grill for high heat and lightly oil the grate. Remove tuna steaks from the marinade and shake off excess; reserve marinade for basting.

Cook tuna steaks on the preheated grill for 5 to 6 minutes. Flip steaks and baste with reserved marinade. Continue cooking until desired doneness, about 5 minutes more. Discard any remaining marinade.

Serve and enjoy!