Heat oven to 450. Place a rack on a baking sheet and spray with nonstick cooking spray.
Whisk together egg whites and mustard in a shallow dish. In a second dish, blend the panko and cheese. Place the flour in a third dish.
Coat the chicken with the flour, shaking off the excess. Dip in the egg mixture and then coat well with the panko. Place on prepared rack.
Bake at 450 for 15 minutes and turn over. Bake additional 10 minutes or until internal temperature registers 160 on an instant read thermometer. Run under broiler for 1 minute if you wish to lightly brown.
Serve with heated marinara sauce. Accompany with cooked french fries and prepared cole slaw, if desired.