Boil the pasta water. Fill a large pot with water, bring to a rolling boil, and add 1/2 teaspoon salt. Add fettuccine and cook until al dente. Scoop out 1/4 cup pasta water and drain.
Season the chicken. Pat the chicken breasts dry and sprinkle both sides with Italian seasoning, garlic powder, 1/2 teaspoon salt, and 1/4 teaspoon black pepper.
Sear the chicken. Heat olive oil in a skillet over medium-high heat. Cook chicken in a single layer for 4–5 minutes per side until golden and cooked through. Rest for 5 minutes before slicing.
Start the sauce. Reduce heat to medium, add butter to the skillet, and melt. Add minced garlic; sauté until fragrant.
Create the Alfredo sauce. Gradually add heavy cream and chicken broth to the skillet. Bring to a gentle simmer, then stir in Parmesan cheese until smooth. Season with remaining salt and pepper.
Finish the dish. Add cooked fettuccine to the sauce, tossing to coat. Add pasta water, if needed, to achieve a thick, glossy consistency. Garnish with parsley.