Place chicken breasts between two sheets of plastic wrap. Pound gently to ¼-inch thickness.
Prepare three shallow bowls: flour in the first, beaten eggs and milk in the second, and panko with Parmesan in the third.
Season chicken with salt and pepper. Dredge in flour, dip in egg wash, then coat with breadcrumb mixture.
Heat olive oil in a skillet over medium-high heat. Sear chicken 2–3 minutes per side until golden. Transfer to a baking dish.
Spoon marinara sauce over each piece. Top with mozzarella and extra Parmesan.
Bake at 400°F (200°C) for 10–12 minutes, until cheese is bubbly and golden.
Rest for 5 minutes, garnish with fresh basil, and serve warm.
