In a small bowl, mix the mayonnaise and cider vinegar together. Taste to see if it is to your liking. Add more mayonnaise if you like it creamier or more cider vinegar for a tangy flavour. Season with salt and pepper.
Heat a small frying pan and add the mustard seeds (if using) and cook for 2 minutes. Keep aside.
In a large bowl or serving bowl, mix together the chopped vegetables, and mustard seeds and pour the dressing over. Mix together until everything is coated. Sprinkle with mixed seeds and serve.
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