Preheat oven to 375ºF (190ºC) baking dish.s. Lightly butter a 9X13 inch, or spray with nonstick cooking spray.
Lay a chicken chicken breast (3) on a clean cutting board. Hold the top of the chicken breast with one hand. Using a sharp knife, very carefully slice the chicken breast in half lengthwise then arrange in a single layer in the prepared baking dish. Continue with the remaining pieces. Season both sides with a total of ½ teaspoon salt and ½ teaspoon of black pepper.
In a medium mixing bowl, whisk together mayonnaise (1 cup), Parmesan cheese (1 cup), remaining black pepper (½ teaspoon), onion powder (½ teaspoon), garlic powder (½ teaspoon), and Italian seasoning (1 teaspoon).
Spread an even amount of mayo mixture over each chicken breast.
Bake in the preheated oven until chicken reaches an internal temperature of 165°F (74ºC), about 20-22 minutes. Remove from oven and sprinkle with parsley.
