In a small bowl, combine the salt, paprika, garlic, pepper, and thyme; blend well. Sprinkle both sides of the steak with the dry rub and then rub it in. Let the meat sit for half an hour at room temperature.
To cook on a charcoal grill, light the charcoal (preferably hardwood) in a chimney starter. Pour the hot coals into the grill so that the coals are banked to one side. Put the grill grate on the grill. When the coals are coated in gray ash and you can hold your hand 1 to 2 inches above the grate for 2 seconds, set the meat directly above the coals to sear it until dark grill marks form, about 3 minutes per side. Or, heat one area of a gas grill on high and another on low. Set the meat on the grates on the high side and sear it until dark grill marks form, about 3 minutes per side.
When the steak is nicely marked by the hot grill on both sides, move the meat away from the coals (or to the cooler side of a gas grill) and cover the grill so it can cook indirectly. Remove the steak from the grill when it's slightly firm to the touch and registers 130° to 135°F on an instant-read thermometer for medium rare (about another 5 to 8 minutes), or 140° to 145°F for medium.
Let the steak rest on a cutting board for at least 5 minutes before carving. To serve, trim the fat from the steak and slice the meat on the diagonal into thin strips. Serve with warm tortillas and roasted tomato salsa and let your guests assemble their own tacos.