Thaw frozen vegetables in the microwave (or place entire bag in a bowl of hot water for about 10 minutes). Set aside until step 6.
Heat oil in a large wok or sauté pan on medium heat. Add ginger, garlic, and scallions, and stir fry until cooked, but not brown, about 2–3 minutes.
Add the rice vinegar, chili sauce, and brown sugar to the pan, and bring to a simmer.
In a bowl, mix cornstarch with chicken broth, and add to the pan. Bring to a boil over high heat, stirring constantly. Lower temperature to a gentle simmer.
Add chicken, and stir continually for 5–8 minutes.
Add vegetables, and mix gently. Simmer with lid on to reheat, about 2 minutes.