Blend parsley, garlic, oregano, red wine vinegar, olive oil, red pepper flakes, and lemon juice in a food processor. Pulse until finely chopped.

Coat flank steak with half the chimichurri sauce. Let marinate for at least 30 minutes.

Preheat the grill to high heat. Cook the steak for 4-5 minutes per side for medium-rare.

Let the steak rest for 5 minutes before slicing against the grain.

Drizzle remaining chimichurri over the sliced steak before serving.