Mix parsley, oil, lemon juice, garlic, crushed red pepper and 1/4 tsp. salt in a bowl.
Prepare steak: Preheat a gas grill to high for 20 minutes; oil when hot.
Sprinkle steak with salt. Grill steak for 4 to 6 minutes, flip and continue to cook until done, 3 to 4 minutes more for medium rare, depending on thickness of meat and heat of grill. (Or, cook in batches on stovetop on a lightly oiled, ridged grill pan over medium-high heat.)
Transfer steak to cutting board, tent loosely with foil and let stand 5 minutes. Slice and spoon chimichurri on top to serve.
