To prepare a wood or charcoal fire: Ignite about 5 qt. mesquite or other hardwood chunks or charcoal using an electric or chimney starter. When the fire is well established, bank the coals to one side of the grill. (Grill the tomatoes and chiles for the salsa directly over the coals now, while they are still very hot). Let the coals burn down until they're covered with gray ash and no flames are visible (this will take 30 to 40 minutes from the time you bank the coals). An oven thermometer set on the grill grate opposite the coals should read 250ºF to 275ºF after the grill lid has been on for a few minutes. Toss over the coals a handful of mesquite chips that have been soaked in water for about an hour.
To prepare a gas grill: Follow the manufacturer's instructions for setting it up for indirect grilling and smoking.
Brush the steaks lightly with the lime juice and season with salt. Put the steaks on the cooler zone of the grill (as far from the coals as possible) and cover the grill. Cook, turning once after 15 minutes, until the steaks are charred and well done yet tender, about 30 minutes.
While the steaks are grilling, prepare the pico de gallo. Just before the meat is done, slice the avocado, if using. Remove the meat from the grill and chop or slice it very thinly. Serve with the pico de gallo, the avocado or guacamole, the salsa, and the warm tortillas.