Heat a nonstick frying pan over a medium-low heat and dry-fry the cashew nuts for 5–8 minutes, stirring frequently, or until golden brown and toasted. Tip on to a small plate and leave to cool. Add the mustard seeds to the pan and dry-fry for 1–2 minutes or until they start to pop.
Mix together the mustard seeds, carrots, red pepper, chervil and spring onions in a large bowl.
Whisk together all the dressing ingredients in a small bowl, then pour on to the grated carrot salad. Mix thoroughly to coat and heap into serving bowls.
Chop the cashew nuts coarsely and scatter over the salad. Serve immediately.