Place beef Flat Iron 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, 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.
Nutrition information per serving: 59 Calories; 27 kcal Calories from fat; 3 g Total Fat; 1 g Saturated Fat; 1 g Monounsaturated Fat; 12 mg Cholesterol; 134 mg Sodium; 5 g Total Carbohydrate; 0.6 g Dietary Fiber; 4 g Protein; 0.5 mg Iron; 0.5 mg NE Niacin; 0.1 mg Vitamin B6; 0.8 mcg Vitamin B12; 1.3 mg Zinc; 5.4 mcg Selenium;