Preheat your oven to 375°F (190°C).

Bring a large pot of salted water to a boil. Cook penne according to package directions but stop 1–2 minutes before al dente. Drain well, reserving 1/2 cup of pasta water.

Heat olive oil in a large oven-safe skillet over medium-high heat. Season chicken cubes with salt, pepper, and Italian seasoning. Cook, stirring occasionally, until golden and the internal temperature reaches 165°F (74°C), about 5–6 minutes. Transfer to a plate and set aside.

In the same skillet, add garlic and sauté for 30 seconds until fragrant. Stir in marinara sauce, heavy cream, and sun-dried tomatoes. Bring to a gentle simmer. Add spinach and cook until wilted, about 1 minute. Season with salt and pepper to taste.

Return the cooked chicken to the skillet. Add drained pasta, half of the mozzarella, and half of the Parmesan. Toss well to coat everything in the sauce. If the mixture looks too thick, stir in a splash of the reserved pasta water to loosen it.

Smooth the top into an even layer. Scatter the remaining mozzarella and Parmesan over the surface, then sprinkle with panko breadcrumbs if using. Drizzle a tiny amount of olive oil over the breadcrumbs.

Bake uncovered for 20–25 minutes, until the sauce is bubbling and the cheese is melted and golden brown.

Remove from the oven and let the bake rest for 5 minutes. Scatter fresh basil over the top, serve directly from the skillet or baking dish.