Making the Teriyaki Sauce: In a medium sized saucepan add the soy sauce, sugar, cider vinegar, garlic, ginger, and pepper. In a small bowl whisk together cornstarch and water. Slowly whisk into soy sauce mixture and bring to a boil over medium high heat. Reduce to a simmer and let thicken for about 3-5 minutes.
In a 9x13 casserole dish add the chicken breasts. Pour half of the teriyaki sauce on top and bake for 25 minutes or until chicken is cooked throughout and no longer pink. Remove from oven and shred the chicken.
Stir in cooked rice and add vegetable mixture. Pour in remaining sauce. Mix together and baked until heated through for about 10-15 minutes.