Step 1: Pat the skirt steak dry with paper towels. This helps the marinade adhere better and promotes a better sear.
Step 2: In a large bowl or a resealable plastic bag, whisk together the soy sauce, olive oil, lime juice, minced garlic, brown sugar, red pepper flakes (if using), and black pepper until well combined.
Step 3: Add the skirt steak to the marinade, ensuring it is fully coated. If using a bowl, cover it tightly with plastic wrap.
Step 4: Marinate in the refrigerator for at least 30 minutes, or up to 8 hours. For maximum flavor and tenderness, 2-4 hours is ideal. Do not marinate for longer than 8 hours, as the acid can start to break down the meat too much.
Step 5: About 20-30 minutes before grilling, remove the steak from the refrigerator to allow it to come closer to room temperature. This promotes more even cooking.
Step 6: Preheat your grill to high heat (450-500°F / 230-260°C). Clean the grill grates thoroughly and lightly oil them to prevent sticking.
Step 7: Remove the skirt steak from the marinade, letting any excess drip off. Discard the remaining marinade.
Step 8: Place the skirt steak directly on the hot grill. Cook for 2-4 minutes per side for medium-rare (internal temperature 130-135°F / 54-57°C). Adjust cooking time for desired doneness. Skirt steak cooks quickly, so watch it closely!
Step 9: Once cooked, transfer the skirt steak to a cutting board and tent it loosely with foil. Let it rest for 5-10 minutes. This allows the juices to redistribute, ensuring a tender and juicy result.
Step 10: Slice the steak against the grain into thin strips. Serving against the grain is vital for tenderness with skirt steak.