Begin by bringing a large pot of salted water to a boil. Add the fettuccine pasta and cook according to package instructions until al dente. Drain the pasta and set it aside, reserving a bit of the pasta water for later.
In a large skillet, heat the olive oil over medium-high heat. Add the diced chicken breast and season with Cajun seasoning, salt, and pepper. Cook for about 5-7 minutes, or until the chicken is golden brown and cooked through. Remove the chicken from the skillet and set it aside.
In the same skillet, add the sliced bell pepper, diced onion, and minced garlic. Sauté for about 3-4 minutes, or until the vegetables are tender and fragrant.
Reduce the heat to medium-low and pour in the heavy cream and chicken broth, stirring to combine. Allow the sauce to simmer for a couple of minutes until it thickens slightly.
Return the cooked chicken to the skillet and add the cooked fettuccine. Toss everything together until the pasta is well coated with the creamy sauce. If the sauce is too thick, add a splash of the reserved pasta water to reach your desired consistency.
Stir in the grated Parmesan cheese until melted and creamy. Taste and adjust the seasoning with additional salt and pepper if needed. Finish with a sprinkle of chopped parsley for a fresh touch.