Place a small skillet over medium heat, add the chopped hazelnuts and toast until golden, stirring and flipping them about for about 5 minutes. While the nuts are toasting, juice the lemon into a salad bowl and add the mustard and some salt and pepper. Whisk in the extra-virgin olive oil in a slow steady stream. Add the shredded carrots, red onion, currants and parsley. Toss to coat in the dressing and sprinkle with the toasted hazelnuts.