01 - Preheat oven to 400°F and line a baking sheet with parchment paper.
02 - Place each chicken breast between two sheets of plastic wrap and pound to 1/2-inch thickness.
03 - Arrange three shallow bowls: one with flour; one with whisked eggs and milk; one with breadcrumbs mixed with Parmesan, garlic powder, oregano, salt, and pepper.
04 - Coat each chicken breast in flour, shake off excess, dip in egg mixture, then coat with breadcrumb mixture.
05 - Heat olive oil in a large skillet over medium-high heat. Fry chicken 2–3 minutes per side until golden brown. Transfer to prepared baking sheet.
06 - Spoon marinara sauce onto each chicken breast, then sprinkle shredded mozzarella and Parmesan cheese on top.
07 - Bake chicken in preheated oven for 15 minutes until cheese is bubbly and chicken reaches 165°F internal temperature.
08 - While chicken bakes, heat olive oil in saucepan over medium heat. Sauté garlic and onion until soft, about 3 minutes. Add crushed tomatoes, basil, oregano, sugar, salt, and pepper. Simmer uncovered for 15 minutes, stirring occasionally.
09 - Bring large pot of salted water to a boil. Cook spaghetti according to package directions until al dente. Drain well.
10 - Divide spaghetti onto plates, spoon marinara sauce over pasta, top with chicken. Garnish with fresh basil and extra Parmesan if desired.