01 - Bring a large pot of salted water to a boil. Cook fettuccine according to package instructions until al dente. Drain and set aside, reserving 1/2 cup pasta water.
02 - Pat chicken breasts dry with paper towels. Rub both sides thoroughly with Cajun seasoning, salt, and black pepper.
03 - Heat olive oil in a large skillet over medium-high heat. Add chicken and cook 5–6 minutes per side until blackened and cooked through (internal temperature 165°F). Remove from pan, cover loosely with foil, and let rest 5 minutes before slicing thinly.
04 - In the same skillet (wipe out excess oil if needed), melt butter over medium heat. Add garlic and sauté 1 minute until fragrant.
05 - Pour in heavy cream, stirring constantly. Bring to a gentle simmer, then add Parmesan cheese, black pepper, and salt. Stir until smooth and thickened, about 3–4 minutes. Add a splash of reserved pasta water if needed for desired sauce consistency.
06 - Toss cooked fettuccine in the Alfredo sauce until evenly coated.
07 - Divide pasta among plates. Top with sliced blackened chicken. Sprinkle with fresh parsley and extra Parmesan. Serve immediately.