Place red and green cabbage, red and yellow bell pepper, snap peas, cucumber, cherry tomatoes, and onion in a mixing bowl.
Whisk vinegar, yogurt, sesame oil, celery seed, sugar, garlic powder, salt, and pepper together in a small mixing bowl until smooth. Pour over vegetables. Toss gently to coat. Cover and refrigerate until chilled and flavors combine, at least 2 hours.