Slice chicken breasts into 1-inch pieces and season generously with 2 tablespoons of Cajun seasoning. Toss to ensure all pieces are coated.

Bring a large pot of generously salted water to a rolling boil. Add the fettuccine or penne pasta and cook according to package directions until al dente. Before draining, reserve 1 cup of the starchy pasta water. Drain the remaining pasta water and set the pasta aside.

While the pasta cooks, heat 1 tablespoon of olive oil in a large skillet (preferably cast iron or a heavy-bottomed pan) over medium-high heat until shimmering. Add the seasoned chicken pieces in a single layer, being careful not to overcrowd the pan (cook in batches if necessary).

Sear the chicken for 3-4 minutes per side until golden brown and cooked through. The internal temperature should reach 165°F (74°C). Remove the cooked chicken from the skillet and set it aside on a plate.

Reduce the heat to medium. Add 1 tablespoon of olive oil and 2 tablespoons of unsalted butter to the same skillet, scraping up any browned bits from the chicken. Add the diced red bell pepper, green bell pepper, and yellow onion.

Sauté the vegetables for 5-7 minutes, stirring occasionally, until they have softened. Add the minced garlic and cook for another minute until fragrant.

Pour in the chicken broth, deglazing the pan by scraping up any remaining flavorful browned bits from the bottom. Bring the broth to a gentle simmer.

Stir in the heavy cream, the remaining 1 tablespoon of Cajun seasoning, dried oregano, dried thyme, smoked paprika (if using), and a pinch of cayenne pepper (adjust to your preferred level of heat). Bring the sauce to a gentle simmer, stirring occasionally.

Reduce the heat to low and gradually whisk in 1/2 cup of grated Parmesan cheese until it is melted and the sauce is smooth. Season the sauce with salt and freshly ground black pepper to taste. If the sauce appears too thick, add a splash of the reserved pasta water until it reaches your desired consistency.

Return the cooked chicken pieces to the skillet with the creamy Cajun sauce. Add the drained pasta and toss everything together to combine, ensuring all the pasta and chicken are thoroughly coated in the rich sauce.

Cook for another 1-2 minutes, stirring gently, allowing the pasta to absorb some of the delicious sauce. If the sauce becomes too thick, add another tablespoon or two of reserved pasta water.

Divide the spicy Cajun chicken pasta among serving plates. Garnish with fresh chopped parsley and additional grated Parmesan cheese, if desired. Serve immediately and enjoy!