Bring a large pot of salted water to a boil. Add the dry pasta and cook according to package directions until al dente. Before draining, carefully scoop out about 1/4 cup of the starchy pasta cooking water and set it aside. Drain the pasta and set it aside.

While the pasta cooks, pat the chicken breast pieces dry with paper towels and season them lightly with a pinch of salt and black pepper taken from the measured amounts.

Heat the olive oil in a large, deep skillet over medium-high heat. Add the seasoned chicken pieces in an even layer and cook for about 5 to 7 minutes, stirring occasionally, until the chicken is lightly browned on the outside and cooked through. Transfer the cooked chicken to a plate and set aside, leaving any juices in the skillet.

Reduce the heat to medium and add the unsalted butter to the same skillet. Once the butter has melted, add the minced garlic and cook for about 30 to 60 seconds, stirring constantly, until the garlic is fragrant but not browned.

Pour the chicken broth into the skillet, scraping up any browned bits from the bottom with a wooden spoon. Let the broth simmer for 1 to 2 minutes to slightly reduce.

Stir in the heavy cream, then add the remaining salt, black pepper, Italian seasoning, and red pepper flakes if using. Bring the mixture to a gentle simmer over medium heat, stirring occasionally, for about 3 to 4 minutes until it starts to thicken slightly.

Reduce the heat to low and gradually sprinkle in the freshly grated Parmesan cheese, stirring constantly until it melts smoothly into the sauce and becomes creamy.

Add the cooked chicken along with any juices from the plate back into the skillet. Stir to coat the chicken in the garlic Parmesan sauce and let it warm through for 1 to 2 minutes.

Add the drained pasta to the skillet and toss gently until all of the pasta is well coated in the sauce. If the sauce seems too thick, add a splash of the reserved pasta cooking water, a little at a time, until you reach your desired consistency.

Taste the Garlic Parmesan Chicken Pasta and adjust the seasoning with a little more salt or black pepper if needed. Remove from the heat, sprinkle the chopped fresh parsley over the top if using, and serve warm.