1. Pat the chicken breasts dry with paper towels. Cut them into 1-inch pieces. In a medium bowl, toss the chicken pieces with 1 tablespoon of Cajun seasoning, ensuring each piece is evenly coated.

2. Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the seasoned chicken and cook for 5-7 minutes, stirring occasionally, until the chicken is browned and cooked through. The chicken should no longer be pink in the center. Remove the cooked chicken from the skillet and set aside.

3. In the same skillet, add the chopped onion and green bell pepper. Cook for 5-7 minutes, stirring occasionally, until the vegetables are softened. Add the minced garlic and cook for another minute until fragrant, being careful not to burn the garlic.

4. Stir in the diced tomatoes (undrained), chicken broth, heavy cream, grated Parmesan cheese, dried oregano, and red pepper flakes (if using). Bring the sauce to a gentle simmer, stirring frequently.

5. While the sauce is simmering, cook the fettuccine or penne pasta according to package directions in a separate pot of salted boiling water until al dente. Reserve about 1/2 cup of the pasta cooking water before draining.

6. Return the cooked chicken to the skillet with the sauce. Stir well to combine. Add the drained pasta to the skillet with the sauce and chicken. Toss everything together until the pasta is thoroughly coated. If the sauce seems too thick, add a splash or two of the reserved pasta water until it reaches your desired consistency.

7. Taste the pasta and adjust seasoning with salt, black pepper, and additional Cajun seasoning if desired. Garnish with fresh chopped parsley and extra grated Parmesan cheese before serving hot.