In bowl, combine vegetables; pour marinade over all.
Marinate in refrigerator for at least 4 hours, stirring occasionally.
Note: if not going to be eaten the same day, perhaps wait to add mushrooms and cucumbers until a few hours before serving — they will go limp instead of remaining crisp.
The balance can be combined and marinated up to a couple of days ahead of serving in the refrigerator.
I have found it works best if you marinate in a tightly covered bowl.
Then when you are in the kitchen and think about it, you can just turn it upside down, shake it a bit, and put it back in the frig instead of stirring it.