In steamer, bring water to a boil. In the meantime, place colander in sink and set up a bowl of ice water.
Cut vegetables to appropriate sizes and have ready. (Note: for this salad it is important to cut vegetables into fairly large pieces--they will hold up better and last longer)
When water is boiling, steam carrots and whole Brussels sprouts and cook for 4 minutes. Then add broccoli, peppers, green beans, mushrooms and onion. Cook for another 4 minutes or until al dente.
Immediately immerse into ice water. Let chill for about 10 minutes and drain well. It is important to drain well, so flavor is not diluted. If possible, lay vegetables out on paper towels and pat dry.
Make marinade by whisking together ingredients in a bowl, adding oil a little at a time.
Put veggies in a glass container or bowl, add marinade, cover and put into refrigerator for at least 1 hour. Enjoy!