Cook the fettuccine pasta according to package instructions until al dente. Drain and set aside.
In a bowl, toss the sliced chicken with the Cajun seasoning until well coated.
In a large skillet, heat the olive oil over medium-high heat. Add the seasoned chicken and sauté for about 5-7 minutes until cooked through and golden brown. Remove the chicken from the skillet and set aside.
In the same skillet, add the sliced onions and bell peppers, sautéing for about 4-5 minutes until they soften. Add the minced garlic and cook for an additional 1 minute until fragrant.
Lower the heat to medium and pour in the heavy cream, stirring to combine. Let it simmer for 2-3 minutes.
Slowly add the grated Parmesan cheese, stirring continuously until the sauce is smooth and creamy. If the sauce is too thick, you can add a splash of pasta water to reach your desired consistency.
Return the cooked chicken to the skillet and add the drained fettuccine pasta. Toss everything together to coat the pasta and chicken in the sauce. Season with salt and pepper to taste.
Cook for an additional 2-3 minutes to heat everything through.
Serve hot, garnished with chopped fresh parsley.
Notes
For extra heat, add more Cajun seasoning or red pepper flakes.