Place 6 boneless, skinless chicken breasts between two sheets of plastic wrap and pound evenly until about ½ inch thick. Season both sides lightly with salt and pepper.
Prepare three shallow bowls: one with 1 cup all-purpose flour , one with beaten 3 large eggs, and one with 2 cups breadcrumbs mixed with grated 1 cup Parmesan cheese .
Dredge each chicken breast in flour, then dip in egg, and finally coat thoroughly with the breadcrumb-Parmesan mixture.
Heat 3 teaspoons olive oil in a large skillet over medium-high heat. Cook chicken until golden brown on both sides, about 3–4 minutes per side. Transfer to a paper towel–lined plate to drain excess oil.
Spread 3 cups marinara sauce in the bottom of a baking dish. Arrange fried chicken breasts on top, spoon more sauce over them, then sprinkle generously with 2 cups mozzarella cheese.
Place the dish in a preheated oven at 375°F (190°C) and bake for 20–25 minutes, until cheese is melted and bubbly.
Remove from the oven, garnish with 1/4 cup basil and serve hot with pasta or a side salad.