Pat the tuna steaks dry and season both sides evenly with the 1/2 teaspoon salt and 1/2 teaspoon pepper.
In a small bowl, whisk together 2 tablespoons olive oil, 2 tablespoons finely chopped parsley, and 1 minced garlic clove until combined.
Pour or brush the parsley-garlic oil over the seasoned tuna steaks, coating both sides.
Preheat a grill or grill pan over medium heat until hot.
Place the tuna steaks on the hot grill and cook for about 5 minutes, then flip and cook an additional 2–3 minutes for medium-rare (internal temperature about 125°F).
Remove the tuna from the grill and let rest for 1 minute, then serve immediately.