Prepare cauliflower as directed on page 634; separate into flowerets. Prepare green beans as directed on page 617ù leave beans whole. Heat 1 inch salted water (1/2 ts salt to 1 cup water) to boiling. Add cauliflowerets and beans. Cover and heat to boiling; reduce heat. Boil until crisp-tender, 6 to 8 minutes; drain.
Place cauliflowerets, beans and onion rings in shallow glass dish. Shake remaining ingredients in tightly covered container; pour over vegetables. Cover and refrigerate, stirring once, at least 4 hours. Drain before serving. 8 servings; 40 calories per serving.