In a medium sauce pan, combine all sauce ingredients except the corn starch. Bring to a boil and cook for 1 minute.
In a small bowl, combine corn starch and 2 tbs water. Add this mixture to what's on the stove and let it cook for 1 minute more, for it to thicken.
Place the chicken in a 9 x 13 baking dish, then pour 1 cup of the sauce over it.
Bake the chicken until cooked through, about 30 minutes. (A little underdone is ok because it's going back in.)
Meanwhile, thaw the vegetables if necessary, otherwise you can chill.
Once cool enough to handle, shred the chicken with two forks. Add the rice, vegetables, and water chestnuts to the baking dish, along with the remaining teriyaki sauce. Stir to evenly mix, then return to the oven to heat though, 15-20 minutes.