In a medium bowl, add the orange juice, lime juice, olive oil, soy sauce, Worcestershire sauce, apple cider vinegar, garlic, red pepper flakes, and ground cumin. Whisk together to combine.
Place the skirt steak in a large baking dish or gallon size zip-top bag and pour the marinade on top. Turn the steak a few times until it's completely coated with marinade, cover, and refrigerate for 2 to 6 hours. Do not marinate for longer than 8 hours because the meat will start to break down.
Remove steak from marinade and discard any excess marinade. Pat steak dry with paper towels and season with salt and black pepper on both sides.
To grill: Preheat grill to high heat (about 450°F-500°F). Grill the skirt steak with the lid closed for about 3-4 minutes per side for medium rare, or longer depending on the thickness and your desired doneness. I recommend using an instant read meat thermometer to make sure it's perfect!
To cook on the stove: Heat a large cast-iron skillet over high heat with a generous drizzle of oil. Add the skirt steak and press down on the meat a couple of times to make sure it's fully touching the bottom of the pan (you want to get a good sear). Cook for 3-5 minutes, then flip and cook for another 3-5 minutes depending on the thickness and your desired doneness. I recommend using an instant read meat thermometer to make sure it's perfect!
Transfer the steak to a cutting board and let it rest for 5 minutes. Slice thinly across the grain and at a slight angle and serve.
Notes
Use a meat thermometer to make sure you don't overcook it. This is my favorite and foolproof way of making sure I never overcook steak.
Let it rest before slicing. This will help to lock in the juices and keep the meat from drying out when slicing.
Slice against the grain. Use a sharp knife to slice the meat against the grain and at a slight angle into thin slices. This helps to further break down the muscle fibers of the meat and makes it easier to chew when eating.