Gather all ingredients.
Preheat the oven to 425 degrees Fahrenheit.
Combine the butter milk and mustard together.
Mix the mustard and buttermilk together.
Add the sliced chicken to the mustard/milk mixture and let it marinate for 5-10 minutes.
Combine the panko, walnuts, Parmesan cheese, rosemary, salt, and pepper in a bowl.
Add the panko mixture in a pan on med-high heat for three minutes or until golden brown.
Place the panko mixture on a plate or in a ziplock bag to coat the chicken slices.
Make sure to coat the chicken evenly.
Add the fully coated chicken to a baking pan to put in the oven.
Cook the chicken for 20 minutes or until golden brown.
Voila! Beautifully golden, baked chicken.
Serve with veggies for a fantastic meal.