Season the flank steak with 1 teaspoon salt and the black pepper and let it stand for 20 minutes.
Stir the parsley, garlic, red wine vinegar, olive oil, crushed red pepper and remaining salt together.
Heat a grill or grill pan over medium-high heat and cook the steak for 4 to 6 minutes per side until it reaches 145°F.
Transfer the steak to a board and rest it for at least 3 minutes.
Slice the steak very thinly across the grain and divide it among the rolls.
Spoon 2 tablespoons chimichurri over each sandwich, keeping most of the loose oil in the bowl.