Preheat the oven to 375ºF.
Take the chicken breasts, and using a sharp knife, cut them in half horizontally, making 6 thinner pieces of chicken. If you have any that are thicker than the others, cover in plastic wrap and use a meat mallet to flatten the breast.
Pat the chicken dry with paper towels, and transfer to a baking sheet. (I like to line it with parchment paper.)
In a bowl, combine the mayonnaise, mustard, sour cream, garlic powder, seasoned salt, and pepper.
In another bowl, combine the panko with the parmesan cheese.
Spread the mayonnaise mixture over the top of each piece of chicken, making sure to cover the whole surface. Sprinkle the panko mixture evenly over the top.
Transfer the baking sheet to the preheated oven and bake until the chicken is cooked through, 15-20 minutes.
Serve topped with fresh parsley.
