Bring a large pot of lightly salted water to a rolling boil. Cook the fettuccini in the boiling water until cooked through yet firm to the bite, about 8 minutes; drain.Advertisement
Cook the bacon in a large, deep skillet over medium-high heat until evenly browned, about 10 minutes; drain on a paper towel-lined plate. Finely chop bacon and set aside.
Melt butter in a large skillet over medium heat. Cook and stir the chicken, onion, and garlic in the butter until chicken is browned, about 5 minutes. Stir in the alfredo sauce, Parmesan cheese, Italian seasoning, and garlic salt; continue to cook and stir until the chicken is no longer pink in the center and the sauce is heated through, about 5 minutes more. Add the chopped bacon and mix to serve.