Heat 1 teaspoon of the oil in 12-inch nonstick skillet over medium-high heat. Add the chicken and cook for 10 minutes or until it's well browned on both sides. Remove the chicken from the skillet.
Heat the remaining oil over medium heat. Add the mushrooms, zucchini and onion and cook until they're tender. Add the garlic and cook for 1 minute. Stir the sauce and vinegar in the skillet and heat to a boil. Return the chicken to the skillet. Reduce the heat to low. Cover and cook for 10 minutes or until chicken is cooked through. Serve with black pepper.