1. Heat olive oil in a large pot over medium heat. Season the chicken with salt, pepper, and Cajun seasoning, then sauté until lightly browned and nearly cooked through. Remove the chicken and set aside.

2. In the same pot, add the diced onion, garlic, celery, carrots, and red bell pepper. Cook until the vegetables have softened, about 5 minutes.

3. Stir in an additional 1 tbsp of Cajun seasoning, then pour in the chicken broth, heavy cream, and diced tomatoes if using. Bring the mixture to a simmer.

4. Add the pasta and cook until al dente, stirring occasionally to prevent sticking.

5. Return the cooked chicken to the pot and stir in the grated Parmesan cheese until melted and well combined.

6. Taste and adjust the seasoning with salt, pepper, or extra Cajun spice if desired.

7. Garnish with chopped fresh parsley before serving.