Combine first 5 ingredients in a small bowl. Toss pork with 1/4 cup sauce mixture in a medium bowl, reserving remaining sauce mixture. Marinate 15 to 30 minutes.
Meanwhile, trim root end of bok choy. Slice white stems; tear or cut large leaves in half.
Heat wok over high heat until a few drops of water evaporate immediately. Swirl 2 teaspoons oil in pan to coat. (If using a nonstick skillet, heat oil over medium-high heat.)
Add pork; stir-fry 3 minutes or until browned.
Transfer to a plate, and wipe wok clean.
Heat remaining 3 teaspoons oil in wok over high heat (medium-high, if using a nonstick skillet).
Add garlic, ginger, and shallots; stir-fry 30 seconds or until fragrant. Stir in bok choy stems, bell pepper, and mushrooms, and cook 5 minutes or until tender.
Stir in reserved sauce mixture. Bring to a boil, reduce heat, and simmer 1 minute or until thickened. Stir in bok choy leaves and pork, and cook until heated through.
