DO-AHEAD TIP: If using bamboo skewers, soak them in water for 30 minutes before use, to prevent burning.
Preheat oven broiler.
In a saucepan, combine the first 6 ingredients (cornstarch through ginger); cook and stir over medium heat until mixture boils and thickens; remove from heat and set aside.
Alternately thread pork cubes, mushrooms and onion wedges onto skewers. Broil kabobs for 20 minutes or until done, turning and brushing often with broth mixture.
Bring the remaining broth mixture to a boil and serve with kabobs.