Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package directions until al dente. Before draining, reserve about 1 cup of the pasta water. Drain the pasta and set aside.

While the pasta is cooking, pat the chicken breast cubes dry with a paper towel. In a medium bowl, toss the chicken with Italian seasoning, garlic powder, salt, and pepper until evenly coated.

Heat 1 tbsp of olive oil in a large oven-safe skillet or Dutch oven over medium-high heat. Add the seasoned chicken in a single layer and cook for 5-7 minutes, turning occasionally, until golden brown and cooked through. Remove the chicken from the skillet and set it aside on a plate.

Reduce the heat to medium. Add the remaining 1 tbsp of olive oil to the same skillet. Add the chopped onion and sauté for 3-4 minutes until softened and translucent.

Add the minced garlic and red pepper flakes (if using) and cook for another minute until fragrant, stirring constantly.

Pour in the chicken broth to deglaze the pan, scraping up any browned bits from the bottom. Add the crushed tomatoes and stir to combine. Bring the sauce to a simmer and cook for 5 minutes to allow the flavors to meld.

Reduce the heat to low. Slowly stir in the heavy cream and grated Parmesan cheese until the sauce is smooth and creamy. Season with additional salt and pepper to taste.

Return the cooked chicken and the drained pasta to the skillet. Stir everything together until the chicken and pasta are well-coated in the sauce. If the sauce is too thick, add a splash of the reserved pasta water until it reaches your desired consistency.

Top the pasta evenly with the torn or sliced fresh mozzarella. You can either cover the skillet with a lid for 2-3 minutes to melt the cheese, or for a bubbly, golden-brown top, place the skillet under the broiler for 1-2 minutes (watch carefully to prevent burning).

Remove from the heat (or broiler), garnish with fresh basil, and serve immediately.