1. Preheat oven to 475° F. Place beans and onion on a large, foil-lined baking sheet. Toss with the oil and arrange in a thin layer.
2. Bake 14 minutes, sprinkle with almonds; toss and bake 5 minutes more, or until almonds are golden.
3. Combine the vinegar and sugar in a small saucepan. Bring to a boil over medium high heat, boil 1 minute or until reduced slightly. Drizzle over the bean mixture. sprinkle with salt and pepper and toss until well coated.