Drain tomatoes, reserving juice for marinade. Set aside diced tomatoes with green chiles.
Combine reserved tomato juice, 1/2 cup cilantro, lime juice and olive oil in medium bowl. Cover and refrigerate 1/3 cup marinade for rice. Place beef Flank Steak and remaining marinade in food-safe plastic bag; turn steak to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight, turning occasionally.
Combine rice, reserved 1/3 cup marinade, diced tomatoes, black beans and remaining 1/4 cup cilantro in medium bowl. Season with salt and pepper, as desired. Set aside.
Cut slit lengthwise down 1 side of each poblano pepper to create pocket, leaving stem and tip intact. Make another small crosswise cut just below the stem to form T-shaped opening. Remove and discard seeds and membranes, being careful to keep peppers intact. Spoon rice mixture evenly into peppers. Wrap each tightly in aluminum foil to seal.
Remove steak from marinade; discard marinade. Place steak in center grid over medium, ash-covered coals; arrange peppers around steak. Grill steak, covered, 11 to 16 minutes (over medium heat on preheated gas grill 16 to 21 minutes) for medium rare to medium doneness, turning occasionally. Grill peppers, covered, 25 to 30 minutes (20 to 25 minutes on gas grill) or until peppers are tender and filling is heated through, turning occasionally.
Carve steak across grain into thin slices. Remove peppers from foil. Serve peppers with steaks and toppings as desired.
Nutrition information per serving: 345 Calories; 99 kcal Calories from fat; 11 g Total Fat; 3 g Saturated Fat; 5 g Monounsaturated Fat; 42 mg Cholesterol; 322 mg Sodium; 33 g Total Carbohydrate; 7.6 g Dietary Fiber; 30 g Protein; 4.7 mg Iron; 8.9 mg NE Niacin; 1.2 mg Vitamin B6; 1.4 mcg Vitamin B12; 5 mg Zinc; 34 mcg Selenium; 96.8 mg Choline;