Place the bread in the bowl of a food processor and process until fine crumbs are formed, about 25 to 30 seconds. Put the crumbs on a baking sheet and bake for 12 minutes, until golden. (You will wind up with about 1 1/3 cups toasted crumbs.)
In a medium bowl, toss the crumbs with oregano, garlic powder, paprika, 1/4 teaspoon salt and 1/4 teaspoon pepper. In another bowl, whisk the egg whites and milk together. In a third bowl stir together the flour, and the remaining 1/4 teaspoon salt and 1/4 teaspoon black pepper. Dip each piece of chicken, 1 piece at a time, in flour, shaking off excess, then egg, then bread crumbs, shaking off excess.
Increase oven temperature to 400 degrees. Place breaded breasts in a glass baking dish and spray on each side with cooking spray, about 5 seconds total per side. Bake breasts until cooked though and crumbs are browned, about 15 minutes. Top with marinara sauce, mozzarella and parmesan and return to oven for an additional 10 minutes, until cheese is bubbling.