01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with cooking spray or oil.
02 - Spread the cooked chicken evenly in the bottom of the prepared baking dish.
03 - Pour marinara sauce evenly over the chicken. Sprinkle with dried Italian herbs if desired for extra flavor.
04 - Layer mozzarella cheese and half of the Parmesan cheese over the sauce, ensuring even coverage.
05 - In a small bowl, combine panko breadcrumbs with melted butter until evenly moistened. Stir in chopped parsley if using.
06 - Sprinkle breadcrumb mixture evenly over the cheese layer. Top with remaining Parmesan cheese for extra flavor.
07 - Bake uncovered for 25-30 minutes, or until the topping is golden brown and the cheese is bubbly.
08 - Let the casserole stand for 5-10 minutes before serving to allow the layers to set for easier serving.