In a large resealable plastic bag, combine all the marinade ingredients and add the meat, making sure it’s evenly and coated throughout. Seal and refrigerate for 2-3 hours, no longer than 3 hours.
Once it’s marinated, remove from the fridge and let it sit at room temperature for 30 minutes prior to grilling.
Make the corn salsa: In a bowl, combine all corn salsa ingredients until evenly combined. Set aside.
Heat a grill or grill pan(if doing indoors) over high heat. Shake off any excess marinade and grill the skirt steak for about 3-4 minutes per side for a medium rare, about 130-135 degrees F using an instant meat thermometer.
Transfer steak to a plate and let rest for 10 minutes, loosely covered with foil to keep warm.
Slice steak: The grain lines in skirt steak run parallel to the shorter side of the meat, but you need to slice perpendicular to the grain to ensure it’s tender. To do so, cut the steak into 3-4 smaller pieces parallel to the grain lines. Then, slice each smaller piece perpendicular to the grain (against the grain).
Serve over warm tortillas and top with the prepared corn salsa and guacamole. Enjoy!