In a large skillet, saute onion and garlic in oil for 3-4 minutes or until tender. Add chicken; cook for 6-8 minutes or until chicken juices run clear. Stir in the tomatoes, peppers, olives, salt and oregano; bring to a boil. Reduce heat; cover and simmer for 10-12 minutes, stirring occasionally.
Combine cornstarch and water until smooth; gradually stir into chicken mixture. Bring to a boil; cook and stir for 1 minute or until thickened. Serve with rice. Yield: 6 servings.