Preheat the oven to 450 degrees. In a small saucepan, combine the ingredients for the tomato sauce. Simmer over medium-low heat as you prepare the chicken.
In a pie plate, beat the eggs with the milk. In 2 more pie plates (or shallow dishes), spread the flour and panko. Season the panko lightly with salt and pepper. Pat the chicken dry and season with salt and pepper. Lightly dredge each chicken breast in the flour (this seals and keeps moist), followed by the egg, and finishing with the panko. Press to help the crumbs adhere.
In a large skillet, heat the oil over medium-high heat until shimmering. Add the chicken and cook, turning once, until cooked through, about 7 minutes. Drain the chicken on a paper towel-lined plate, then transfer to a lightly greased baking dish.
Top the chicken with the tomato sauce, two cheeses, pepperoni and parsley. Bake the chicken for about 15 minutes, until the cheese is melted and bubbling.