Place the skirt steak on a cutting board and beat it thoroughly on both sides using a meat mallet. This step helps break down the muscle fibers for a more tender bite.

In a large bowl or measuring cup, mix together the olive oil, red wine vinegar, lime juice, soy sauce, Maggi sauce, salt, pepper, and Mexican oregano. Stir well until fully combined.

In a large dish, layer half of the steak. Pour half of the marinade over the steak and top with half the diced onion and garlic. Add the remaining steak, then pour over the rest of the marinade and top with the rest of the onion and garlic.

Cover and refrigerate for 6-8 hours.

Preheat your grill over medium heat for about 5 minutes. Grill the steak for 5 to 7 minutes per side, depending on your desired doneness. Transfer to a tray, cover, and let rest for 5 minutes before slicing.