Bring salted water to a boil and cook fettuccine until al dente. Drain and set aside.
Season chicken with Cajun seasoning. Sear in olive oil and butter over medium-high heat until cooked through, about 5–6 minutes per side.
Remove chicken, let rest, then slice into strips.
In the same skillet, melt butter and sauté garlic for 1 minute.
Add heavy cream and simmer 3–4 minutes until thickened. Stir in Parmesan until smooth.
Toss fettuccine in the sauce. Adjust consistency with reserved pasta water if needed.
Top with sliced Cajun chicken, sprinkle parsley, and serve warm.
