Heat oil in stockpot over medium heat until hot. Brown beef Shanks, in batches, on all sides. Remove beef from pan. Pour off drippings. Combine broth, 1/2 cup fish sauce, 1/4 cup sugar, lemon grass, cilantro, soy sauce and garlic in stockpot; bring to a boil. Return shanks to stockpot. Reduce heat; cover tightly and simmer 1-1/2 to 2-1/4 hours or until shanks are fork-tender.
Meanwhile, combine 1 cup sugar, vinegar, fish sauce, ginger, lemon grass and cilantro sprigs in medium saucepan. Bring to a boil over medium heat. Remove from heat; strain liquid and cool. Combine carrots, peppers and vinegar mixture in large bowl. Cover and refrigerate for 1 hour or until ready to serve.
Remove shanks from stockpot. When cool enough to handle, cut beef from bones. Combine vegetable mixture, tomatoes and beef in large bowl; strain excess liquid. Serve beef mixture over greens. Garnish with fried shallots, if desired.
Nutrition information per serving: 607 Calories; 96.3 kcal Calories from fat; 10.7 g Total Fat; 3.3 g Saturated Fat; 0 g Trans Fat; 0.6 g Polyunsaturated Fat; 5.3 g Monounsaturated Fat; 99 mg Cholesterol; 4698 mg Sodium; 78 g Total Carbohydrate; 4.3 g Dietary Fiber; 52 g Protein; 9.7 mg Iron; 1060 mg Potassium; 9.5 mg NE Niacin; 0.9 mg Vitamin B6; 5 mcg Vitamin B12; 13.8 mg Zinc; 42.9 mcg Selenium; 19.8 mg Choline;