Finely chop the parsley, cilantro, fresh oregano and garlic (or process in a food processor for several pulses). Place in a small bowl.
Stir in the olive oil, vinegar, salt, pepper and red pepper flakes. Adjust seasonings to taste.
Serve immediately or refrigerate for up to a week. Always return to room temperature before serving.
Season skirt steak well with freshly ground black pepper and kosher salt.
Grill for 3 minutes on each side over high heat to give it the caramelized char on the outside and juicy center.
Sprinkle with Maldon sea salt before serving and serve with chimichurri sauce.