This dish is one of the many things that put Texas on the worldwide culinary map. If you can't find outside skirt steak in your area, many companies are happy to sell you some online. However, you owe it to yourself to try the real thing at some point. Substituting flank or sirloin can be delicious, but they are not the real thing. When adequately prepared, outside skirt steak is tender and delicious, especially when cooked over Mesquite. Once you've cooked and sliced the skirt steak, eat it immediately. In restaurants, fajitas are served on a sizzling iron platter to keep the meat warm longer. You can replicate this by having everything else done before you cook the skirt steak and by placing your serving platter in a warm oven.
Preheat propane grill or start a fire with Mesquite wood/charcoal in Weber type outdoor grill.
Clean silver skin (if any) from the skirt steak
Place the skirt steak between two pieces of plastic wrap to prevent splattering.
Tenderize skirt steak with a meat mallet or heavy wooden rolling pin - I've even used a large unopened soup can or heavy iron skillet in a pinch.
On a large oven sheet pan, spread the Salsa Negra over one side of the skirt steak. Season liberally with Southwest Seasoning. Reserve
Preparing Peppers and Onions
Core and seed the peppers and slice thin lengthwise.
Peel and core a whole onion. Slice in half and then slice thinly lengthwise.
Use a saute or frypan over medium-high heat, add the vegetable oil and bring it up to temperature. Add the sliced onions and sliced peppers and saute until tender. Add the garlic and cook until fragrant 1-2 minutes. Add the southwest seasoning mix and toss to coat the vegetables well. Deglaze with the sherry wine and cook for another minute. Turn off the heat and cover with a lid or aluminum foil to keep warm. Reserve. (Before you serve, squeeze the fresh lime juice on top)
Grilling the Skirt Steak
Prepare a gas grill by turning on a high or Mesquite charcoal grill. Then, using Mesquite, start the fire and allow the nice bed of hot coals to form.
Over a hot grill, carefully place the skirt steak with the Salsa Negra over the hot coals or grill. Promptly cover the other side of the skirt steak with more Salsa Negra using a basting brush. Apply more Southwest Seasoning.
Cook the skirt steak until good char marks show. The meat should be sizzling hot through the process. On my grill, it takes about 3-4 minutes per side. (This is a thin cut of meat, be mindful of overcooking.)
Remove the skirt steak from the heat when it's cooked. Allow the meat to rest on a cutting board for 2-3 minutes before slicing.
Cut the skirt steak down to workable portions about 4 inches long. Turn and slice against the grain to ensure tenderness.
Serve immediately over the cooked onions and peppers on a pre-warmed platter or dish.
Serve with the condiments you desire. Serve the fajitas with one or all of the following: green sauce, pico de gallo, onions and peppers, fresh grilled tomato and jalapeño, shredded Oaxaca or sharp cheddar cheese, guacamole, sour cream, finely minced onions mixed with cilantro, thinly sliced radish or pickled Nopales, wedges of lime and warm flour or corn tortillas.