Prep the oven and pan: Heat the oven to 400°F (200°C). Lightly oil a 9x13-inch baking dish, or line it with parchment for easy cleanup.

Cook the pasta (optional): If using, boil in well-salted water until just shy of al dente. Drain and toss with a splash of olive oil to prevent sticking. Set aside.

Season the chicken: Cut chicken into bite-size pieces. Pat dry, then toss with 2 tablespoons olive oil, 1 teaspoon salt, 1/2 teaspoon black pepper, 1 teaspoon Italian seasoning, and half the minced garlic.

Quick roast the chicken: Spread the chicken on a sheet pan in one layer. Roast for 10–12 minutes until just cooked through. It will finish in the casserole, so don’t overcook.

Mix the sauce: In a bowl, combine marinara, remaining garlic, 1 teaspoon Italian seasoning, and a pinch of red pepper flakes if you like heat. Taste and add salt or pepper as needed.

Build the base: If using pasta, spread it in the baking dish and spoon half the sauce over top. Scatter half the mozzarella and a sprinkle of Parmesan.

Add the chicken: Layer the roasted chicken evenly over the base. Pour over the remaining sauce, then top with the rest of the mozzarella and the 1/2 cup Parmesan.

Make the crunchy topping: Stir panko with melted butter, 1 tablespoon olive oil, a pinch of salt, and a little black pepper. For extra flavor, add 1 tablespoon grated Parmesan and a pinch of Italian seasoning. Sprinkle over the casserole.

Bake: Place the dish on the center rack and bake 18–22 minutes, until the cheese is bubbling and the topping is golden brown.

Finish and rest: Let it rest for 5–10 minutes so it sets up a bit. Shower with chopped basil or parsley for freshness. Serve hot with extra Parmesan on the side.