Bring a large pot of salted water to a boil. Add the penne pasta and cook until al dente according to package instructions, usually around 10 minutes. Drain the pasta and set it aside.
Heat olive oil in a large skillet over medium heat. Add the diced onion and sauté until softened and translucent, about 5 minutes. Stir in the minced garlic and cook for another 1-2 minutes until fragrant.
Pour in the crushed tomatoes and stir to combine. Add the Italian seasoning, salt, and pepper. Lower the heat and let the sauce simmer gently for 10 minutes to develop flavor.
Slowly stir in the heavy cream, mixing until the sauce turns a lovely creamy pink. Fold in the diced cooked chicken, heating through for 3-4 minutes.
Add the drained penne to the skillet with the sauce. Toss everything together until the pasta is evenly coated.
Preheat your oven to 375°F (190°C). Transfer half of the pasta mixture to the baking dish. Sprinkle half of the Parmesan and mozzarella cheeses over the layer. Add the remaining pasta on top, then finish with the rest of the cheeses.
Place the baking dish in the oven and bake for 20-25 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it rest for a few minutes. Garnish with fresh basil leaves before serving.