In a medium bowl toss pork strips with five-spice powder and ginger. Coat an unheated 4- to 6-quart nonstick Dutch oven with cooking spray. Heat over medium-high heat. Add pork strips. Cook for 4 to 6 minutes or until pork is browned, stirring occasionally. Remove pork from pan and set aside.
In the same pan cook carrots, mushrooms, and celery in hot oil over medium heat for 5 minutes, stirring occasionally. Add water and broth. Bring to boiling. Add soba; return to boiling and cook, uncovered, for 3 to 4 minutes or until noodles are just tender.
Meanwhile, in a small bowl combine flour and soy sauce until smooth. Add to noodle mixture along with bok choy, snow peas, green onions and cooked pork. Cook and stir until just boiling; cook and stir for 1 minute more. Remove from heat. Stir in orange juice just before serving. Ladle mixture into four serving bowls.