Preheat a grill pan to medium-high heat. Drizzle the steak with some oil and sprinkle with salt and pepper. Grill for 7 minutes on each side.
Meanwhile, whisk the remaining 1/4 cup olive oil, the parsley, vinegar and garlic in a bowl and season with salt and pepper.
Remove the steak from grill and rest it for 10 minutes. Slice the steak against the grain and serve with the parsley sauce.