Cut beef with grain into 2-inch strips; cut strips across grain into 1/8-inch slices. (Beef is easier to cut if partially frozen, 30 to 60 minutes.) In medium bowl, mix broth, soy sauce, Sichuan sauce and red pepper. Stir in beef. Let stand 10 minutes.
Drain beef; reserve marinade. Heat 12-inch nonstick skillet over medium-high heat. Add half of the beef to skillet; stir-fry 2 to 3 minutes or until brown. Remove beef from skillet. Repeat with remaining beef. Return all beef to skillet.
Add reserved marinade, the tomatoes and bean sprouts to beef in skillet; stir-fry about 1 minute or until vegetables are warm. Sprinkle with cilantro.