For Dressing: In a glass jar with a tight fitting lid combine the vinegar, sugar and salt. Screw on lid and shake vigorously until the salt and sugar has dissolved. Add the remaining dressing ingredients and shake vigorously until emulsified. Dressing will last up to 3 weeks in the refrigerator.
In a medium serving bowl, combine the carrots, onion, and dressing; toss to coat. Taste and season with salt and pepper, if needed.