In a medium bowl, whisk together olive oil, soy sauce, red wine vinegar, Worcestershire sauce, minced garlic, brown sugar, smoked paprika, black pepper, salt, and crushed red pepper flakes until smooth and well combined.

Place the skirt steak in a resealable plastic bag or a shallow dish. Pour the prepared marinade over the steak, ensuring it is evenly coated. Seal the bag tightly or cover the dish, then refrigerate for at least 2 hours (preferably overnight).

Approximately 15 minutes before grilling, preheat your grill or grill pan to high heat (around 450°F). Make sure the grill grates are clean and lightly oiled.

Once marinating is complete, remove the skirt steak from the refrigerator, allow the excess marinade to drip off and discard the marinade.

Place the skirt steak directly on the preheated grill. Grill for 3-4 minutes on one side until a nice char forms. Flip the steak and continue grilling for an additional 3-4 minutes for medium-rare doneness.

Once cooked to your liking, remove the skirt steak from the grill and let it rest for 5-10 minutes before slicing.

After resting, slice against the grain into thin strips and serve immediately, garnished with fresh cilantro or parsley if desired.