Preheat oven to 425°F. Spray a rimmed baking pan with nonstick cooking spray or line with parchment paper.
In a small bowl, mix together panko, garlic powder, and ¼ teaspoon pepper. Add olive oil to panko mixture, mixing until bread crumbs are coated. Set aside.
½ cup panko bread crumbs, 2 teaspoons olive oil, ¼ teaspoon garlic powder, ½ teaspoon coarse black pepper, divided
Place a chicken breast on a flat surface. Carefully make a horizontal cut, not cutting all the way through. Open the chicken up so it lies flat, still hinged on one side. Use a mallet or the heel of your hand to lightly pound the chicken so it’s about a quarter inch thick, as evenly as possible.To minimize mess, place a layer of plastic wrap on top of the chicken before you pound it. Season the butterflied chicken with salt and ¼ teaspoon pepper.
3 boneless skinless chicken breasts, ¼ teaspoon kosher salt
Arrange ham slices over one half of each chicken breast. Layer cheese slices on top of ham slices.
4 ounces sliced deli ham, 4 ounces sliced Swiss cheese
Fold chicken over the ham and cheese, tucking in any stray ham or cheese. Place chicken on baking pan, sides not touching.
Smear the top of each chicken breast with about ½ teaspoon Dijon mustard each. Cover with panko mixture. Pat to adhere.
1 ½ teaspoons Dijon mustard
Bake for 30 to 35 minutes or until chicken is cooked through and breading is light golden brown. Internal temp with an instant read thermometer should be at least 165°F.
Cut each breast in half crosswise to make 6 servings.
Video
Notes
How to butterfly chicken: If you're unsure about how the chicken should look when butterflied, refer to the photos in the post.
Add a sauce: If you'd like to serve your chicken with a sauce, see chicken cordon bleu kabobs for a delicious sauce recipe.
Homemade panko: Make your own panko homemade bread crumbs for the breading, if desired.
Mustard options: Any coarse ground or stone ground mustard can be substituted for the Dijon.