Boil Spaghetti noodles until done, but firm. Drain, cool by covering with cold water. Drain.
Add chopped vegetables and enough dressing to coat noodles. Stir.
To make Poppy Seed Dressing, combine sugar, mustard, salt and vinegar in the top of a double boiler. Heat over hot water until sugar is dissolved. Put into blender and slowly blend in onion juice and salad oil. Add poppy seeds at the end.