Season the skirt steak or flank steak with sea salt and let it come to room temperature before cooking. Pat it dry thoroughly to ensure a good sear. Grill or cook over high heat until browned on the outside and juicy on the inside (2–3 minutes per side). Let rest, then slice into thin strips. Gently heat the guajillo sauce (do not use it as a marinade) and pour it over the cooked meat. Serve with corn tortillas, white onion, cilantro, and lime if desired.
