A rubdown with seasoned salt and pepper before grilling develops the rich, beefy taste of sirloin steak or tip roast, while a hot oak fire seals in all the flavor. Even inexpensive skirt steak can stand up to direct-heat cooking once the meat's been tenderized in a spicy lime juice marinade. Cover meat and place in the refrigerator overnight. Sear meat over hottest part of fire, then move it to slightly cooler part of grill and cook, uncovered, until meat tests done. Carve thin slices of meat on a cutting board with grooves to catch any juices.
Transfer slices to a warm platter and moisten with juices.
Adding aromatic chunks, chips or sawdust to the coals will further enhance the flavor of the meat. Serve the fajitas with plenty of salsa and, if you like, guacamole and sour cream. Cover and marinate in refrigerator for at least 2 hours or overnight. Prepare a hot charcoal fire. Leave peels on onions, cut in half lengthwise, and lightly coat with oil.