Slowly whisk onion soup mix and white wine vinegar together in a bowl. Whisk in sugar, cider vinegar, oil, salt, and black pepper until well incorporated. Add zucchini, celery, and green bell pepper; toss to coat.
Cover bowl with plastic wrap and refrigerate, stirring occasionally, for 4 to 6 hours. Drain off excess liquid before serving.
All done! Now take a photo, rate it, and share your accomplishments!