Rinse chicken breast and let drain completely.
Whisk together egg, milk, salt and pepper in a bowl for dipping mixture.
Pour breadcrumbs into a separate bowl.
Dip each chicken breast into egg mixture, then coat thoroughly with breadcrumbs.
Pre-heat frying pan with oil on medium-high temperature.
Once oil is hot, cook chicken breast for 5 minutes on each side until golden brown.
Place cooked chicken on an oven-safe dish and pour heated tomato sauce over each fillet.
Grate mozzarella cheese generously on top of each fillet.
Turn oven to broil and place chicken under broiler until mozzarella is melted and golden brown.
Remove from oven and serve immediately over spaghetti with additional tomato sauce.