In a large resealable plastic bag or shallow glass container, combine the first four ingredients. Remove 1/3 cup and set aside. Add pork to remaining marinade; seal bag or cover container and turn to coat. Refrigerate for 1 hour. In a large skillet or wok over medium-high heat, stir-fry half of the pork in 1 tablespoon oil for 2 to 3 minutes or until no longer pink. Remove pork with a slotted spoon; set aside. Repeat with remaining pork and oil. In the same skillet, stir-fry the asparagus for 2 to 3 minutes or until crisp-tender. Stir cornstarch into reserved marinade; add to the skillet. Bring to a boil; cook and stir for 2 minutes or until thickened. Return pork to skillet and heat through. Serve over rice if desired.