Cut the turkey into 6 equal portions, about 4 oz. each. Place them in a zip-lock bag.
Mix together the mustard, wine, and garlic pepper, then add to the zip-lock bag.
Close the bag, then massage the contents with your hands to completely cover the turkey with the marinade.
Once the turkey is well-coated, place the bag in the refrigerator to marinate for at least 4 hours.
Preheat the oven to 450°F and cover a baking sheet with parchment paper.
Combine the panko, hazelnuts, Herbes de Provence, and pepper on a large plate.
Remove one portion of turkey from the marinade and transfer immediately to the plate, coating both sides of turkey with the panko mixture.
Once coated, place the turkey on the baking sheet and repeat with the remaining portions of turkey.
Roast the turkey in the oven for 25 to 30 minutes until cooked all the way through but still juicy.