Combine marinade ingredients in small bowl. Reserve 2 tablespoons for topping. Place beef Flat Iron Steaks and remaining marinade in food-safe plastic bag; turn steaks to coat. Close bag securely and marinate in refrigerator 15 minutes or up to 2 hours, turning occasionally.
Meanwhile, combine corn, tomato, 2 tablespoons cilantro, salt and reserved 2 tablespoons marinade in medium bowl. Cover and refrigerate.
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.
Remove steaks; keep warm. Place tortillas on grid. Grill, covered, 1 to 2 minutes or until toasted. Turn tortillas over; sprinkle evenly with cheese. Grill 1 to 2 minutes or until toasted and cheese starts to melt.
Carve steak into thin slices. Season with salt, as desired. Top tortillas with equal amounts of steak and corn mixture. Garnish with cilantro, if desired.
Nutrition information per serving: 485 Calories; 207 kcal Calories from fat; 23 g Total Fat; 11 g Saturated Fat; 7 g Monounsaturated Fat; 100 mg Cholesterol; 726 mg Sodium; 33 g Total Carbohydrate; 4.4 g Dietary Fiber; 33 g Protein; 2.9 mg Iron; 7.8 mg NE Niacin; 0.4 mg Vitamin B6; 5.3 mcg Vitamin B12; 8.9 mg Zinc; 36.5 mcg Selenium; 106.9 mg Choline;