Preheat oven to 400°F and spray a 9x13 inch baking dish with nonstick cooking spray.
Pat chicken breasts dry with paper towels to remove excess moisture.
Arrange chicken breasts in a single layer in the prepared baking dish.
In a medium bowl, whisk together mayonnaise, ½ cup Parmesan cheese, minced garlic, onion powder, kosher salt, and black pepper until smooth.
Spread the mayonnaise mixture evenly over the chicken breasts.
In a small bowl, stir together panko breadcrumbs and melted butter until crumbs are well coated.
Sprinkle the buttered breadcrumbs evenly over the top of the mayo-coated chicken.
Bake uncovered for 25 to 30 minutes until breadcrumbs are golden and the chicken reaches an internal temperature of 165°F.
Remove from oven and garnish with chopped fresh parsley.
Let the chicken rest for 5 minutes before serving to allow juices to redistribute.