Cut carrot, bell pepper and celery into 1 1/2 -inch matchstick pieces. Thinly slice onion. Set vegetables aside separately.
Combine vinegar, soy sauce, sesame oil, sugar, chili oil and cornstarch in small bowl; reserve. Fill wok or large fry pan with oil to a depth of 1 1/2 – 2 inches. Place over high heat until oil reaches about 375° F. Add beef, half at a time; deep- fry for 1 minute until brown, turning occasionally. Lift out; drain on paper towels; reserve. Cook remaining beef. Remove all but 2 tablespoons oil from wok. Reheat oil over high heat until hot.
Add carrot and onion; cook, stirring constantly for 1 minute. Add bell pepper and celery; stir-fry for 1 more minute. Stir in sauce and beef. Cook and toss until well mixed.