Place chicken and vegetables in a 3-qt. slow cooker; sprinkle with oregano. Pour sauce over top. Cook, covered, on low 4-5 hours or until chicken is tender., Remove chicken; break up slightly with 2 forks. Return to slow cooker. Serve with spaghetti. If desired, top with olives and cheese. Freeze Option: Place the first 6 ingredients in a freezer container and freeze. To use, place container in refrigerator 48 hours or until contents are completely thawed. Cook and serve as directed.