Place beef steaks and 1/2 cup salsa in food-safe plastic bag; turn steaks to coat. Close bag securely and marinate in refrigerator 15 minutes to 2 hours. Combine remaining 1/2 cup salsa and chopped cilantro, as desired; cover and refrigerate until ready to use.
Remove steaks from marinade; discard marinade. Place steaks on grid over medium, ash-covered coals. Grill, covered, 10 to 14 minutes (over medium heat on preheated gas grill, covered, 12 to 16 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
Carve steaks into thin slices; cut slices into bite-size pieces. Arrange chips on platter. Top each chip evenly with reserved salsa mixture, beef and guacamole. Garnish with cilantro leaf, if desired. Serve immediately.
One pound beef top loin steaks or top sirloin, cut 3/4 inch thick may be substituted for flat iron steaks. Grill top loin steaks 10 to 12 minutes (over medium heat on preheated gas grill, covered, 7 to 10 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Grill top sirloin steak 13 to 16 minutes (over medium heat on preheated gas grill, covered, 8 to 13 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally.
