Combine marinade ingredients in small bowl. Place beef Flank Steak and 1/3 cup marinade in food-safe plastic bag; turn to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight, turning occasionally. Refrigerate remaining marinade.
Remove steak; discard marinade. Brush bell peppers with some of remaining marinade. Place steak and peppers on grid over medium, ash-covered coals. Grill steak, covered, 11 to 16 minutes (over medium heat on preheated gas grill, 16 to 21 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Grill peppers 12 to 15 minutes or until tender, turning occasionally. Brush steak and peppers occasionally with remaining marinade; do not brush during last 5 minutes.
Carve steak across the grain into thin slices. Season with salt. Serve with peppers.
Nutrition information per serving: 234 Calories; 99 kcal Calories from fat; 11 g Total Fat; 3 g Saturated Fat; 4 g Monounsaturated Fat; 66 mg Cholesterol; 246 mg Sodium; 9 g Total Carbohydrate; 1.2 g Dietary Fiber; 24 g Protein; 1.8 mg Iron; 7.4 mg NE Niacin; 0.7 mg Vitamin B6; 1.4 mcg Vitamin B12; 4.5 mg Zinc; 27.6 mcg Selenium; 94.6 mg Choline;