Using a meat mallet or heavy wooden spoon, pound chicken breasts to 1/2-inch thickness between two pieces of wax paper. Set aside.
Line up three shallow bowls. In the first, combine the flour, salt and pepper. In the second, beat the eggs with a splash of water. In the third, combine the breadcrumbs and Parmesan cheese. Thoroughly coat each breast with flour mixture, followed by the egg mixture, followed by the breadcrumb mixture. Place on a cutting board.
Preheat oven to 350 degrees F. Coat a 9x13 baking dish and coat it with cooking spray. Spread half of the marinara sauce on the bottom of the pan in an even layer.
Heat olive oil in a skillet over medium-high heat. Cook the coated breasts in the hot oil one at a time for 1 minute, 30 seconds on each side, or until golden brown. Transfer breasts to the prepared baking dish and place side by side over the marinara sauce as they finish cooking.
Top with the remaining sauce, mozzarella slices and Parmesan cheese. Bake in the preheated oven for 15 minutes. Serve over cooked spaghetti noodles.