Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the rotini, and return to a boil. Cook uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 8 minutes. Drain well in a colander set in the sink.
Stir together the rotini, chicken, and mozzarella cheese in a large casserole dish. Pour the marinara sauce over the pasta mixture; sprinkle with bread crumbs. Cover the dish with aluminum foil.
Bake in the preheated oven until the cheese is entirely melted, about 35 minutes.
