Cook green beans in boiling water to cover 8 minutes or until crisp-tender; drain. Plunge into ice water to stop the cooking process; drain.
Process vinegar and next 5 ingredients in a blender until smooth. With blender running, pour oil through top opening in a slow, steady stream, and process until smooth.
Combine beans, bell pepper strips, and onion. Pour vinaigrette over vegetables, tossing gently to coat. Sprinkle with pecans. Serve chilled or at room temperature.