1. Preheat oven to 400°F. Line a large baking sheet with aluminum foil and spray with cooking spray. Set aside.
2. Pound the chicken breasts so that they are about ½-inch thick. In a shallow dish, combine milk and Dijon mustard stirring with a whisk. Add the chicken to the milk turning to coat. Set aside.
3. Pulse walnuts in a food processor until they resemble fine crumbs.
4. In another shallow dish, combine finely chopped walnuts with the panko bread crumbs, parsley, basil, Parmesan cheese, rosemary and 1/4 teaspoon salt and 1/4 teaspoon black pepper.
5. Remove chicken from milk mixture and dredge in crumb mixture. Lay the chicken on top of the aluminum foil lined baking sheet.
6. Arrange potatoes, carrots, broccoli and bell peppers around the chicken and sprinkle with 1/8 teaspoon kosher salt and 1/8 teaspoon black pepper. Drizzle olive oil over the chicken and vegetables.
7. Bake for 15 minutes, then remove from oven and flip chicken and stir veggies. Bake for an additional 15 minutes or until chicken is no longer pink. Serve immediately.