Dried chipotle powder may be found on the spice aisle of your supermarket. If you serve the flank steak without the Guacamole Sauce, reduce the chipotle powder to 1 tsp. to moderate the heat.
Sprinkle steak evenly with chipotle powder and salt; rub with garlic.
Grill steak, covered with grill lid, over medium-high heat (350° to 400°) 8 to 10 minutes on each side or to desired degree of doneness. Cover loosely with aluminum foil, and let stand 5 minutes.
Cut steak diagonally across the grain into thin strips. Serve with tortillas, if desired, and Guacamole Sauce.
Note: For testing purposes only, we used McCormick Gourmet Collection Chipotle Chile Pepper for dried chipotle powder.