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, pressing to adhere.
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, reaching an internal temperature of 165°F. Remove from pan, cover loosely with foil, and let rest 5 minutes before slicing thinly.
04 - In the same skillet, melt butter over medium heat. Add minced garlic and sauté 1 minute until fragrant, being careful not to burn.
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 reserved pasta water as needed to achieve desired consistency.
06 - Add cooked fettuccine to the skillet with Alfredo sauce. Toss vigorously with tongs until noodles are evenly coated.
07 - Divide pasta among serving plates. Top with sliced blackened chicken. Sprinkle generously with fresh parsley and extra Parmesan cheese. Serve immediately while hot.