Combine first 9 ingredients; stir well with a whisk. Set aside.
Place a 12-inch nonstick skillet over medium-high heat. Coat pan with cooking spray; add chicken, and cook 2 minutes or until chicken is done. Remove from pan; set aside.
Add oil to pan. Add onion and bell pepper; cook 3 minutes, stirring frequently. Add mushrooms and broccoli; cook 3 minutes. Add cooked chicken and soy sauce mixture. Bring to a boil; reduce heat, and simmer, uncovered, 1 minute or until slightly thickened, stirring constantly