Wash beans; trim ends, and remove strings.
Place 1/2 cup water in a large Dutch oven; bring to a boil. Add green beans; cover, reduce heat, and simmer 10 minutes or until crisp-tender. Plunge beans immediately into ice water for 5 minutes; drain. Place beans in a large bowl. Add tomato and onion; toss well.
Combine vinegar and next 3 ingredients in a small bowl, stirring well. Pour vinegar mixture over vegetable mixture; toss gently. Cover and marinate in refrigerator at least 3 hours, stirring occasionally. Sprinkle with cheese just before serving. Serve with a slotted spoon.