1In a large bowl, combine the first 5 ingredients; remove half and set aside. Add beef to remaining marinade; cover and refrigerate for 15 minutes.
In large skillet or wok, stir fry vegs in oil for 2 minutes; remove and keep warm.
Drain and discard the marinade. In the same skillet, stir fry the beef till no longer pink. Add the oranges and reserved vegs. Combine the cornstarch and reserved marinade until smooth; add to skillet. Bring to a boil; cook and stir for 2 minutes or until thickened. Serve over hot rice.