Cook zucchini in 2 cups boiling salted water in saucepan for 1 minute; drain.
Cook frozen peas and onions according to package directions.
Pre- pare salad dressing mix according to package direc- tions.
Combine 1/2 cup dressing with cooked vegetables; add vinegar.
Cover; chill for at least 4 hours, stirring occasionally.
Line chilled salad bowl with salad greens; spoon in marinated vegetables.