If desired, cut beans in half crosswise. Place beans in 2-quart microwave-safe bowl. Add 1/2 cup water; cover with microwave-safe waxed paper. Microwave on High for 10 to 12 minutes or until crisp-tender. Drain. Rinse with cold water to cool; drain well.
Meanwhile, in medium bowl, combine all dressing ingredients; mix well.
Add beans and onion to dressing; toss to coat. Cover; refrigerate at least 1 hour before serving to blend flavors.