Grate the carrots using a food processor or box grater.
Dice the apple.
Toast the walnuts (optional).
In a large bowl, whisk together the lemon juice, Dijon mustard, olive oil, salt, and pepper.
Add the grated carrots, diced apple, and toasted walnuts to the dressing and toss to combine.
Serve the French carrot salad as a side dish or light meal.
