Step 1: In a medium bowl, whisk together olive oil, red wine vinegar, parsley, cilantro, minced garlic, oregano, red pepper flakes, salt, pepper, and lime juice to create the marinade and sauce.
Step 2: Place the skirt steak in a large dish and pour half of the herb mixture over it, ensuring both sides are coated. Reserve the other half of the sauce for serving.
Step 3: Let the steak marinate at room temperature for at least 30 minutes, or in the refrigerator for up to 4 hours.
Step 4: Preheat a cast-iron skillet or outdoor grill to high heat. The surface should be slightly smoking.
Step 5: Remove the steak from the marinade and pat it dry with paper towels to ensure a better sear. Season with an extra pinch of salt if desired.
Step 6: Place the steak on the hot surface and sear for 3-4 minutes per side for medium-rare. Skirt steak is thin, so it cooks very quickly!
Step 7: Remove the steak from the heat and let it rest on a cutting board for at least 5-10 minutes to allow the juices to redistribute.
Step 8: Slice the steak thinly against the grain (perpendicular to the muscle fibers) and drizzle with the reserved chimichurri sauce before serving.