Toss chicken in cornstarch. Heat oil in a large skillet or wok set over medium-high heat. Add chicken and brown on all sides. Add remaining ingredients, except broccoli, and simmer until a lightly-thickened sauce forms around the chicken. Stir in broccoli and heat through. Serve with steamed rice.
Note: To blanch broccoli, plunge into boiling water and cook two minutes. Remove and cool in cold water. Drain well and pat dry.