Preheat your oven to 400 degrees Lightly coat a baking sheet with cooking spray. Cut each chicken breast in half lengthwise so that you have 4 pieces total. Pound each piece to an even 1/2-inch thickness. Set aside.
In a wide, shallow bowl (a pie dish works well), combine the Italian breadcrumbs, whole wheat Panko breadcrumbs, Parmesan, garlic powder, and pepper. In a separate bowl, whisk together the egg whites until lightly foamy. Cut the mozzarella into 4 slices, or grate and divide into four equal portions.
Arrange your workstation in the following order: pounded chicken, egg whites, breadcrumb mixture, baking sheet. Working one at a time, dip each piece of chicken into the egg whites, shaking off any excess, then the breadcrumbs, gently patting the chicken as needed so that the crumbs stick to all sides. Place on the prepared baking sheet. Lightly coat the tops of the chicken with baking spray.
Bake until the chicken is cooked through (it should reach an internal temperature of 165 degrees F) and the crumbs are brown about 15 minutes. Remove from the oven, spoon 2 tablespoons of sauce over each piece of chicken, and top with a slice of mozzarella. Return to the oven and bake until the cheese is melted about 3-5 additional minutes. Sprinkle with basil and enjoy immediately, topped with extra sauce as desired.