Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the cooked rotini pasta, shredded chicken, marinara sauce, garlic powder, Italian seasoning, salt, and black pepper. Mix until well combined.
Transfer the mixture to a greased 9x13-inch baking dish. Spread it evenly.
Sprinkle the mozzarella cheese and Parmesan cheese over the top of the pasta mixture.
If using, mix the breadcrumbs with olive oil and sprinkle them over the cheese layer for added crunch.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for a few minutes. Garnish with fresh basil if desired before serving.