Here's one version:
Oaxacan Style Carne Asada (Mexican-Style Thin Sliced Grilled Steak)
2 bunches scallions, trimmed
8 jalapeno, serrano or poblano chiles
Coarse kosher or sea salt
Fresh ground pepper
2 pound boneless sirloin steak, sliced into broad sheets 1/4-inch thick*
16 corn or flour tortillas
4 limes, cut into wedges
* Ask your butcher to cut the sirloin for you on his meat slicer. You may alternatively use skirt steak or flank steak in this recipe.
Roast the scallions and chiles on the grill - either on the cooking grate, or directly on the charcoals (if using wood or charcoal). Remove from heat. Cover scallions with foil and set aside; scrape the skin off the chiles with a sharp knife (placing the chiles in a covered dish to steam for a few minutes immediately upon removing them from the grill, can make peeling them easier, but the steamed chiles will be softer). Cut the chiles in half, scrape out and discard the seeds, cover the chile halves with foil and set aside.
Oil the grill grate. Generously salt and pepper the beef and place it on the hot grate; grill, turning with tongs until cooked as desired (3 minutes per side will be Oaxacan-style well-done). Remove to cutting board, allow to rest for a few minutes (to retain juices) then cut into thin strips, against the grain or cut into 1/2-inch dice.
To serve, lace a few tortillas at a time on the grill to warm them. Set out lime wedges, guacamole, salsa and grilled items.
To eat, place a few pieces of beef on a warm tortilla; place a grilled scallion and a chile half on top; top this with spoonsful of guacamole and salsa and a squeeze of lime juice. Roll the entire thing up and eat.