1In 2-quart saucepan, heat 1/2 cup water to boiling over high heat. Add green beans; cover and return to boiling. Reduce heat; simmer covered 10 to 12 minutes or until tender. Drain; cool in colander under cold running water.
2Meanwhile, in shallow bowl, stir vinegar, sugar, salt and pepper until sugar is dissolved. Add onion; toss to coat. Let stand 10 minutes, tossing occasionally. Drain, reserving 1 tablespoon vinegar mixture.
3In medium serving bowl, place beans; top with onion. Drizzle with reserved vinegar mixture and the oil; toss to coat.