Preheat the oven to 375 degrees and lightly grease a 9x13 baking dish.
Cook the penne pasta in a large pot of salted boiling water until al dente, then drain and return it to the pot.
Add the cooked diced chicken, marinara sauce, Italian seasoning, salt, and black pepper to the pasta. Stir until everything is evenly coated.
Mix in half of the mozzarella cheese and all of the Parmesan cheese until combined.
Spread the mixture into the prepared baking dish and sprinkle the remaining mozzarella cheese evenly over the top.
Scatter the panko breadcrumbs over the cheese layer.
Bake for 20 to 25 minutes until the cheese is melted and the breadcrumbs are lightly golden. Let the casserole rest for 5 minutes before serving.