Servings: 3 - 4
Mix all the dressing ingredients together.
Place the red onion slices in a small bowl and cover with cold water. Pour out the water in 10 minutes, and cover again in cold water. Drain again in 10 minutes. This is done because red onions have a strong flavor, and this process will make them milder, and still add a mild onion taste and red color to the bean dish.
Trim the ends of the green beans, and leave whole. Place the beans in a medium-large pot and cover with water. Add salt to the water and bring beans to a boil. Reduce heat, let them simmer for 5 minutes. Remove from the heat and let them sit for another 10 minutes. Test for tenderness. You will want them to be slightly crunchy as they will continue to "cook" in the marinade dressing.
When the beans are cool, drain them in a colander and place the green beans and red onions in a bowl or zip lock bag (a zip lock bag is preferable for marinating), and pour the dressing over the beans and onions. Mix well to cover green beans with dressing. Refrigerate. Stir the bean mixture periodically in the bowl, or just turn over the zip lock bag so all parts are marinated evenly. Marinate for at least 3 to 4 hours or longer before serving. Serve cold or at room temperature.