Cut the beef across prominent grain into 1/4 inch thick slices. In a large bowl, combine soy sauce, cornstarch, sugar, sesame oil, and crushed red pepper; stir until smooth. Add the beef and toss to coat. Set aside. Cut green, red, and yellow peppers lengthwise in half. Remove stems and seeds. Rinse, dry and cut into 1/2 inch strips. Cut onion in half, then into 1 inch pieces. Finely chop garlic. Set aside. Heat wok over high heat about 1 minute or until hot. Drizzle 1 tablespoon vegetable oil into the wok and heat for 30 seconds. Add pepper strips and stir fry until crisp tender. Remove to a large bowl. Add 1 tablespoon vegetable oil and half of the beef mixture to the wok. Stir fry until well browned. Remove the beef to the bowl with the peppers. Repeat with remaining 1 tablespoon vegetable oil and the beef mixture. Reduce heat to medium. Add onions and stir fry about 3 minutes or until softened. Add garlic and stir fry 30 seconds. Return the beef, peppers, and any accumulated juices to the wok; heat through. Spoon rice into a serving dish; top with the beef and vegetable mixture.