Preheat oven to 350°F. Spray a 9x13-inch baking pan with non-stick spray.
In a small saucepan, combine soy sauce, water, brown sugar, ginger, and garlic. Bring to a boil over medium heat, then cook for 1 minute.
Whisk cornstarch with 2 tablespoons water until smooth. Stir into boiling sauce and cook until thickened. Remove from heat.
Place cubed chicken in prepared pan. Arrange steamed vegetables around chicken. Pour 1 cup of sauce over everything.
Cover tightly with foil and bake for 30 minutes, until chicken reaches 165°F internally.
Remove foil and shred chicken in dish using two forks. Add cooked rice and most of remaining sauce, reserving some for serving.
Gently toss everything together. Return to oven uncovered and bake 10 more minutes until heated through.
Let stand 5 minutes before serving. Garnish with sliced green onions and sesame seeds if desired.