Bring a large pot of salted water to a boil and cook pasta until al dente according to package instructions. Reserve 1 cup of pasta water before draining.

While the pasta cooks, heat olive oil in a large skillet over medium-high heat. Add sliced sausage and cook until browned, about 4–5 minutes. Remove sausage to a plate.

Add cubed chicken (if using) to the same skillet and cook until just cooked through, about 5 minutes. Season lightly with salt and pepper. Return the sausage to the pan.

Sauté onion and red bell pepper in the skillet until soft and slightly caramelized, about 4 minutes. Add garlic and cook for 30 seconds until fragrant.

Sprinkle Cajun seasoning and smoked paprika over the mixture and stir for 30–45 seconds to toast the spices.

Pour in the chicken broth and simmer for a minute, scraping up any browned bits from the bottom of the pan. Lower the heat and stir in the heavy cream.

Add the Parmesan and stir until silky.

Combine the drained pasta with the sauce, adding reserved pasta water if the sauce needs loosening. Taste and adjust seasoning.

Finish with chopped parsley and an extra sprinkle of Parmesan. Serve immediately while the sauce is warm.