This is an unusual marinade from the Mexican state of Baja that includes soy sauce, an ingredient you don't think of as Mexican, but which has been used on that country's Pacific coast since the 1500s.
Mix all the marinade ingredients together and submerge the skirt steak in it, making sure every bit is coated with the marinade. Let this sit in the fridge for at least 1 hour, and up to 5 hours.
When you are ready to grill, get your fire very hot. While this is happening, heat up your tortillas on a comal or heavy skillet; keep them warm in a tortilla warmer or wrapped in kitchen towels.
Remove the steak from the marinade and pat the meat dry with paper towels. Make sure it's pretty dry. Rub oil all over the meat.
Sear the skirt steak on the grill for only about 2 minutes per side, tops. Let it rest for a few minutes before slicing. My trick is to cut the skirt steak with the grain into sections, then slice across the grain to get thin, tender slices for your tacos. Serve the skirt steak with cilantro and a little cheese.