Start by preheating your oven to 375°F (190°C). If you haven’t cooked your pasta yet, boil it according to package instructions until al dente, then drain. Shred your cooked chicken if it’s not already shredded and set aside.
In a large mixing bowl, combine the cooked shredded chicken, cooked pasta, marinara sauce, mozzarella cheese, Parmesan cheese, Italian seasoning, garlic powder, salt, and pepper. Gently fold everything together until the pasta and chicken are evenly coated in the sauce and cheese.
Lightly oil your casserole dish or spray it with non-stick spray. Pour the chicken and pasta mixture into the dish and spread it out evenly. Smooth the top with a spatula for an even bake.
In a small skillet, heat the olive oil over medium heat. Add the breadcrumbs and toast them, stirring frequently, until golden brown and crisp, about 3-4 minutes. Sprinkle the toasted breadcrumbs evenly over the casserole. This adds a fantastic crunchy topping that contrasts beautifully with the creamy layers.
Place the casserole in your preheated oven and bake uncovered for 20-25 minutes, or until the cheese is melted, bubbly, and the breadcrumbs are golden. If you like an extra browned top, you can broil for an additional 1-2 minutes, watching carefully to prevent burning.
Once out of the oven, sprinkle the chopped fresh basil over the top for a fresh, herby finish. Let the casserole cool for 5 minutes before serving to allow it to set slightly. Grab a serving spoon and dig in!