Pour vinegar over onions in a small bowl. Let sit while you dice and prep remaining vegetables
Put all remaining salad ingredients in a large bowl, toss
Take onion out of vinegar and toss with remaining salad ingredients. Mix remaining dressing ingredients with vinegar and stir well. Set aside 1/3 of dressing. Pour remaining dressing on salad and stir to coat.
Store in refrigerator overnight. Pour on remaining dressing just before serving. Stir to coat.