In a large bowl, whisk together olive oil, red wine vinegar, minced garlic, oregano, smoked paprika, salt, and black pepper to create the marinade.
Place the skirt steak in a resealable plastic bag or a shallow dish and pour the marinade over the meat, ensuring it is well coated. Seal the bag or cover the dish and refrigerate for at least 2 hours, preferably overnight for maximum flavor.
While the steak is marinating, prepare the chimichurri sauce. In a separate bowl, combine chopped parsley, cilantro, red pepper flakes (if using), lemon juice, and a pinch of salt. Slowly drizzle in ¼ cup of olive oil while stirring until well mixed. Adjust seasoning to taste and set aside.
Preheat your grill or a grill pan over medium-high heat. Remove the steak from the marinade and let it come to room temperature for about 15 minutes.
Grill the skirt steak for about 3-4 minutes on each side for medium-rare, or until it reaches your desired doneness.
Remove the steak from the grill and let it rest for 5 minutes before slicing against the grain.
Serve the sliced steak topped with chimichurri sauce.