In a large pot, bring salted water to a boil and add the pasta. Cook according to the package directions until al dente. Once done, drain the pasta and set it aside, making sure to reserve 1 cup of pasta water for later use.
While the pasta is cooking, take the chicken breasts and generously season both sides with Cajun seasoning, along with salt and pepper to taste.
Heat the olive oil in a large skillet over medium-high heat. Once hot, add the seasoned chicken breasts. Cook for approximately 6–7 minutes per side, or until they are golden brown and fully cooked through. Once done, transfer the chicken to a plate and let it rest before slicing it into strips.
In the same skillet, add the chopped onion and sliced red bell pepper. Sauté for about 4-5 minutes or until the onion turns translucent and soft. Add the minced garlic and continue to sauté for an additional minute, ensuring the garlic becomes fragrant but not burnt.
Pour in the chicken broth, bringing it to a gentle simmer. Use a wooden spoon to scrape up any flavorful browned bits stuck to the skillet. Allow this mixture to simmer and reduce for about 2-3 minutes.
Lower the heat and slowly stir in the heavy cream and freshly grated Parmesan cheese. Mix thoroughly until the cheese has completely melted and the sauce is rich and creamy. If the sauce appears too thick, gradually add the reserved pasta water, mixing until the desired consistency is reached.
Slice the rested chicken breasts and add them back into the creamy sauce. Stir gently to ensure each piece is fully coated in the delightful Cajun sauce.
Add the cooked pasta into the skillet, tossing everything together until well blended. Taste and adjust the seasoning with additional salt and pepper as needed.
Transfer the creamy Cajun chicken pasta to serving bowls immediately. Garnish with a sprinkle of chopped fresh parsley for a refreshing touch and a splash of color.