How to Make It
Preheat oven to 375°F. Cook pasta according to package directions for al dente pasta. Drain and rinse under cool water; set aside to drain well.
Place marinara, shredded chicken, mozzarella, and, if using, crushed red pepper in a large bowl. Add pasta, and toss gently to combine. Transfer to a lightly greased 13- x 9-inch glass or ceramic baking dish. Stir together panko, Parmesan, parsley, olive oil, salt, and pepper in a small bowl, and sprinkle evenly over pasta mixture.
Bake in preheated oven until bubbly and topping is browned, about 35 minutes.
If making ahead:
Follow instructions through step 3. Cover with aluminum foil, and chill up to 24 hours. Bake, covered with foil, at 375°F until hot and bubbly, about 45 minutes. Uncover, and continue to cook until topping is browned, about 10 minutes more.