Bring a large pot of salted water to a boil. Cook rigatoni until al dente. Drain and reserve ½ cup pasta water.
Season chicken with Cajun seasoning, salt, and pepper.
Heat olive oil and butter in a large skillet over medium-high heat. Cook chicken until golden, crispy, and cooked through. Remove and set aside.
In the same skillet, melt butter over medium heat. Add garlic and sauté until fragrant.
Pour in heavy cream and simmer gently for 2–3 minutes.
Reduce heat and stir in Parmesan cheese until smooth.
Add cooked pasta and crispy chicken to the sauce. Toss to coat, adding pasta water as needed.
Taste and adjust seasoning. Serve hot.