In a large glass dish mix the Orange Juice, soy sauce, parsley, onions, oregano, garlic, olive oil, lemon juice and pepper.
Add the tuna steaks and tun to coat them well.
Cover the glass dish and refrigerate for 30 minutes turning the steaks halfway through to re coat with the marinade.
Preheat your grill for high heat.
Lightly oil the cooking grate. Cook the tuna steaks for 4-6 minutes then turn them over carefully and brush with the marinade. Then discard the remaining marinade.
Cook for an another 6 minutes, or to desired doneness.
Notes
If you don't like rare fish, you can grill the tuna a little longer until it is opaque throughout. The tuna will not be as tender, and its texture will be more like a well-done steak, but it will still taste delicious. Make sure not to overcook the tuna or it will become tough.