Heat olive oil in a large skillet over medium-high heat until shimmering.
Season the chicken pieces with salt and black pepper.
Add the chicken to the skillet and cook for 5-6 minutes, stirring occasionally, until golden brown and cooked through. Remove chicken from skillet and set aside.
Reduce heat to medium and add minced garlic to the skillet. Cook for 1 minute until fragrant, stirring constantly to avoid burning.
Pour in the chicken broth and whole milk, stirring to combine.
Add the uncooked penne pasta to the skillet. Stir well to submerge the pasta in the liquid.
Bring the mixture to a boil, then reduce heat to a simmer. Cover and cook for 12-15 minutes, stirring occasionally, until the pasta is tender and most of the liquid is absorbed.
Return the cooked chicken to the skillet and stir to combine.
Add the grated Parmesan cheese, dried Italian seasoning, crushed red pepper flakes, and unsalted butter. Stir until the cheese and butter have melted and the sauce is creamy.
Cook for an additional 2 minutes, stirring frequently, to allow the flavors to meld and the sauce to thicken slightly.
Remove from heat and sprinkle chopped fresh parsley over the top before serving.