I actually slice the meat up first and then marinade them with 1/4 cup worcestershire sauce
1 stout beer
1 cup orange juice
1/2 cup pinapple juice
lots of garlic, onion, habanero, pablano
chile powder, salt and pepper
for about 4 hours. Then off to the smoker with either misquite or apple chips. Yes, I lose a few strips into the fire, but I find the flavor more than makes up for it. If all you have is a kettle grill, just soak your chips and then put them on your charcoal and cover. Since you're cooking fast, you don't need to worry about the slow smoking process, just keep the top closed.
Here's a good recipe:
Fajitas In Cilantro, Citrus, and Gold Tequila Marinade
1 pound fajita meat (preferably outer skirt), or flank steak
4 large garlic cloves, minced
3 tablespoons gold tequila
2 tablespoons fresh lime juice
2 tablespoons fresh orange juice
2 tablespoons red wine vinegar
1 1/2 teaspoons freshly grated orange zest
2 teaspoons Gebhardt's (or similar) chili powder, or to taste
salt, to taste
1 teaspoon worcestershire sauce or soy sauce (optional)
1/2 teaspoon black pepper, freshly ground
1/2 teaspoon brown sugar
3 tablespoons olive oil
3 tablespoons chopped fresh cilantro
Rub the meat with the garlic and place in a shallow dish. Mix the tequila, lime juice, orange juice, vinegar, orange zest, black pepper, chili powder, salt, worcestershire or soy sauce and brown sugar, add the oil and mix well. Pour over meat, basting well. Add the cilantro to both sides of the meat. Cover and marinate 2 to 4 hours (don't overmarinate or the meat will "cook" in the acid,) turning occasionally.
Remove meat from marinade and brush excess marinade off meat so that it doesn't steam when grilled and so that the cilantro doesn't burn on the grill.
Grill meat on hot coals approximately 3 to 4 minutes per side (slightly longer for flank steak) or broil in a preheated oven 6 inches from the flame -- grilling is much more authentic and is highly recommended. Do NOT cook too long -- this cut is good only rare to medium rare, IMHO. It is definitely shoe leather when cooked beyond medium. Let stand 5 minutes before serving. Cut meat at a sharp angle (almost parallel to cutting board) across the grain and serve with flour tortillas, guacamole, salsa, sour cream and grilled vegetables like green or yellow onions and bell or poblano peppers and fresh chopped cilantro.
Serves 4 to 6.
I don't know why anyone would put liquid smoke in fajitas. I marinate the steak in lime juice, olive oil, toasted and ground cumin seed and a little Mexican oregano (not Greek) salt and pepper. I guess if I wanted to introduce a smoky flavor I might add some smoked sweet Spanish paprika