Combine Cajun seasoning, smoked paprika, onion powder, black pepper, kosher salt, and garlic powder in a shallow bowl. Toss chicken cubes until evenly coated. Heat olive oil and butter in a large skillet over medium-high heat until butter foams. Add chicken in a single layer and sear undisturbed for 3 to 4 minutes until a golden crust forms. Flip and sear the other side for 2 to 3 minutes. Remove to a plate and set aside.

Bring a large pot of salted water to boil and cook rigatoni according to package directions until just al dente, about 1 minute before the package suggests. Reserve 1 cup of pasta water before draining. Set the cooked pasta aside.

Add minced garlic to the same skillet and stir for about 30 seconds until fragrant. Pour in chicken stock and scrape up browned bits from the bottom of the pan. Reduce heat to medium and pour in heavy cream. Stir in softened cream cheese and let melt for about 2 minutes, stirring occasionally. Sprinkle in Parmesan cheese and red pepper flakes, stirring until smooth and creamy.

Return seared chicken to the skillet and stir gently to coat with sauce. Add cooked rigatoni and toss everything together over low heat. If the sauce is too thick, add reserved pasta water a splash at a time until it reaches desired consistency. Finish with fresh chopped parsley and serve immediately while hot.