Cook green beans in boiling salted water to cover 5 minutes or until crisp-tender; drain. Plunge into ice water to stop the cooking process; drain.
Whisk together oil and next 5 ingredients in a large bowl. Add green beans, chopped bell pepper, water chestnuts, and onion; toss well to coat. Cover and chill 8 hours.
*Substitute 2 (9-ounce) packages frozen whole green beans, cooked according to package directions.