I first rubbed ground cumin, salt and black pepper on the surface of the skirt steak and let it sit for 10-15 minutes. The marinade is lime juice (2 tbs or one lime), olive oil (2 tbs), ground cumin (1 tbs, but use your judgement, we like cumin a lot but it is strong spice), jalapeno pepper (two, seeded and deveined and finely chopped), garlic (3 fat cloves, finely chopped), and fresh cilantro (2-3 tbs, finely chopped including the stem). I also sliced one large onion (halved and then thinly sliced). I placed everything in a Ziploc bag including the meat and let it marinate for several hours or overnight in the refrigerator.
To cook, I took out the steak and if the surface is too wet, I blot it with a paper towel and season it with salt and pepper again (lightly). I use a "grill" pan which has ridges on the bottom to make char marks, and cook the steak for 1 minute on each side for medium (or to your desired doneness) on high flame with a small amount of olive oil. I set the steak aside on a plate and loosely cover it with an aluminum foil. I then cook the onion with all the marinade for 5 minutes on high flame stirring often or until the onion becomes soft and partially browned. I served the steak sliced across the grain, onion, guacamole (homemade), and salsa (store bought, this was not the best. I did not have good tomatoes to make salsa myself).
Roll it up and serve it with black bean corn salad, which was made by my wife a few days ago. We have not had this for a long time and it tasted very good--reminiscent of the one we had in so long ago in California.