Bring a large pot of generously salted water to a boil. Cook the fettuccine until al dente according to package directions. Reserve ½ cup of the pasta water, then drain and set aside.
Season the chicken breasts evenly with Italian seasoning, salt, and pepper.
Heat olive oil in a large skillet over medium-high heat. Add the chicken and cook undisturbed for 5–7 minutes until golden on the bottom. Flip, add butter to the pan, and cook another 5–7 minutes, or until the internal temperature reaches 165°F.
Transfer chicken to a cutting board and let rest for 3 minutes. Slice into ½-inch strips and loosely cover to keep warm.
In the same skillet over medium-low heat, add butter and heavy cream. Whisk until the butter is fully melted.
Add minced garlic, garlic powder, Italian seasoning, salt, and pepper. Whisk until smooth and combined.
Bring the sauce to a gentle simmer (do not boil) and cook for 3–4 minutes, whisking constantly, until slightly thickened.
Stir in the Parmesan cheese until melted and silky. If the sauce becomes too thick, add reserved pasta water a little at a time until desired consistency is reached.
Remove the pan from heat and toss the cooked fettuccine directly into the sauce until fully coated.
Serve the pasta topped with sliced chicken. Garnish with extra Parmesan, black pepper, and fresh parsley if desired.
