Bring a large pot of salted water to a boil. Cook the pasta until just al dente according to the package directions, reserve about 1/2 cup of pasta water, and drain.

Pat the chicken dry and season it with 1 tablespoon of Cajun seasoning. Heat the olive oil in a large skillet over medium-high heat.

Cook the chicken for approximately 3–5 minutes per side, or until browned and cooked through. Transfer it to a plate as soon as it is done.

Reduce the heat to medium and add the butter, onion, and red bell pepper. Cook for 3–5 minutes, until the vegetables begin to soften.

Add the minced garlic and optional smoked paprika. Cook for about 30 seconds, just until fragrant.

Pour in the chicken broth and scrape up the browned bits from the bottom of the skillet. Simmer for 1–2 minutes.

Add the heavy cream and remaining Cajun seasoning. Simmer gently for 3–5 minutes, stirring occasionally, and avoid a vigorous boil.

Stir in the freshly grated Parmesan and cook for 1–2 minutes, until the cheese melts and the sauce becomes slightly thicker.

Return the chicken to the skillet and add the drained pasta. Toss everything until coated, adding reserved pasta water 1 tablespoon at a time if the sauce is too thick.

Taste before adding salt because both Cajun seasoning and Parmesan may contain plenty of salt. Garnish with parsley and serve immediately.