Slice the chicken breasts in half lengthwise to make four thin cutlets. Pound them gently to about ⅓ inch thick. Season with salt and pepper.
Set up three shallow bowls: one with flour, salt, and pepper; another with beaten eggs; and a third with breadcrumbs and parmesan. Dredge each chicken cutlet through the flour, then the egg, and finally the breadcrumb-parmesan mix. Let rest for 5 minutes.
Heat olive oil in a nonstick skillet over medium heat. Sear the chicken 3–4 minutes per side until golden brown. Do not cook fully; it will finish in the oven.
Pour half of the marinara sauce into a 9x13 inch baking dish. Arrange chicken cutlets on top. Spoon remaining sauce over the center of each piece. Sprinkle with mozzarella.
Bake uncovered at 425°F for 15 minutes or until chicken reaches 165°F and cheese is melted and bubbly. Let rest a few minutes before serving.