In a food processor, combine parsley, shallot, garlic, vinegar, olive oil, 1/4 t. each of the salt and pepper. Pulse until combined; set aside.
Heat a gas grill to medium-high heat or prepare a charcoal grill with medium-hot coals. Sprinkle remaining 1/4 t. each salt and pepper over steak. Grill about 8 minutes per side.
Remove steak from grill and place in a glass baking dish; spread the sauce over top and cover dish with foil; allow to sit for 5 minutes. Remove steak from dish and slice. Serve with sauce remaining in baking dish.