01 - Set oven to 400°F. Line a baking sheet with parchment paper.
02 - Heat olive oil in a saucepan over medium heat. Sauté garlic and onion until softened, about 3 minutes. Stir in crushed tomatoes, basil, oregano, salt, pepper, and sugar. Simmer uncovered for 15 to 20 minutes, stirring occasionally. Add parsley if desired and keep warm.
03 - Tap chicken breasts to an even thickness of approximately 0.75 inches. Season both sides with salt and pepper.
04 - Arrange three shallow bowls: flour in the first; beaten eggs mixed with milk in the second; breadcrumbs combined with Parmesan, garlic powder, and oregano in the third.
05 - Dredge each chicken breast first in flour, then dip into the egg mixture, and finally coat thoroughly with the breadcrumb blend.
06 - Heat olive oil in a large skillet over medium-high heat. Fry chicken breasts for 3 to 4 minutes per side until golden brown but not fully cooked. Drain on paper towels.
07 - Place fried chicken breasts on the prepared baking sheet. Spoon generous marinara sauce over each. Top with shredded mozzarella and additional Parmesan.
08 - Bake in the preheated oven for 15 to 18 minutes until internal temperature reaches 165°F and cheese is melted and bubbly.
09 - While chicken bakes, cook spaghetti in boiling salted water until al dente according to package instructions. Drain thoroughly.
10 - Arrange spaghetti on plates, spoon extra marinara sauce atop, and place a chicken breast over the pasta. Garnish with fresh basil or parsley if desired.