In a bowl, combine parsley, cilantro, garlic, red wine vinegar, 1/2 cup of olive oil, red pepper flakes, and salt. Mix well and set aside to let the flavors meld.
Season the flank steak with kosher salt and pepper. Heat 1 tablespoon of olive oil in a skillet over medium-high heat. Cook the steak for about 5 minutes on each side, or until desired doneness. Let it rest for 5 minutes before slicing against the grain.
Toast the ciabatta pieces lightly (I usually use my oven broiler). Place slices of provolone cheese on the bottom halves and melt under a broiler if desired. Add slices of steak on the cheese, top with a generous amount of chimichurri sauce, and cover with the top halves of ciabatta.