Combine first 9 ingredients; set aside.
Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot. Add chicken; stir-fry 5 minutes. Add green bell pepper; stir-fry 2 minutes. Gradually stir cornstarch mixture into chicken mixture. Cook over medium heat, stirring constantly, until mixture is thickened and bubbly.
To serve, spoon 1/2 cup rice onto each plate; top evenly with chicken mixture.