Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
In a large bowl, mix together the cooked chicken, cooked pasta, and marinara sauce until everything is evenly coated.
Spread half of the chicken-pasta mixture into the prepared baking dish. Sprinkle with 1 cup mozzarella and half of the Parmesan. Add the remaining chicken mixture and top with the rest of the mozzarella and Parmesan.
In a small bowl, mix the Italian breadcrumbs, melted butter, garlic powder, and Italian seasoning. Sprinkle the mixture evenly over the top of the casserole.
Bake uncovered for 25–30 minutes, or until the cheese is bubbly and the breadcrumb topping is golden brown.
Remove from the oven and let rest for 5 minutes. Garnish with fresh basil or parsley before serving.