In a bowl, whisk together olive oil, soy sauce, lemon juice, minced garlic, black pepper, and salt to create the marinade.
Place the tuna steaks in a shallow dish and pour the marinade over them, ensuring they are well coated. Let them marinate for at least 10 minutes.
Preheat the grill or grill pan over medium-high heat.
Remove the tuna steaks from the marinade, allowing excess to drip off. Discard the remaining marinade.
Place the steaks on the hot grill. Cook for about 3-4 minutes on each side for medium-rare, or longer if desired.
Use a meat thermometer to check for doneness, aiming for 130°F (54°C) for medium-rare.
Remove the steaks from the grill and let them rest for a few minutes before serving.
Garnish with fresh chopped parsley and serve with sides of your choice.