Step 1: Prepare the chicken. Pat the boneless, skinless chicken breasts dry with paper towels. Slice each breast horizontally to create thinner cutlets, or pound them to an even 1/2-inch thickness. Season both sides generously with 1 tablespoon of Cajun seasoning.
Step 2: Cook the chicken. Heat 1 tablespoon of olive oil in a large skillet or Dutch oven over medium-high heat. Once shimmering, add the seasoned chicken. Cook for 3-5 minutes per side, or until golden brown and cooked through (internal temperature reaches 165°F/74°C). Remove the chicken from the skillet and set aside on a plate. Do not clean the skillet.
Step 3: Sauté the aromatics. Reduce the heat to medium. Add the remaining 1 tablespoon of olive oil to the same skillet, scraping up any browned bits from the chicken. Add the diced bell peppers (red and green) and onion. Sauté for 5-7 minutes, or until the vegetables have softened and the onion is translucent.
Step 4: Add garlic and more seasoning. Stir in the minced garlic and the remaining 1 tablespoon of Cajun seasoning. Cook for another minute, stirring constantly, until the garlic is fragrant. Be careful not to burn the garlic.
Step 5: Deglaze and simmer. Pour in the chicken broth and scrape the bottom of the skillet with a wooden spoon to release any browned bits. Bring the mixture to a simmer and let it cook for 2-3 minutes, allowing some of the liquid to reduce slightly.
Step 6: Create the creamy sauce. Stir in the heavy cream and Parmesan cheese. Bring the sauce to a gentle simmer, then reduce the heat to low. Let it simmer for 5-7 minutes, stirring occasionally, until the sauce has thickened to your desired consistency. Taste and adjust seasoning with salt and black pepper as needed.
Step 7: Cook the pasta. While the sauce is simmering, cook the fettuccine (or pasta of your choice) according to package directions in a separate pot of salted boiling water until al dente. Reserve about 1 cup of pasta water before draining.
Step 8: Combine and serve. Slice or shred the cooked chicken and add it back into the skillet with the creamy Cajun sauce. Add the drained pasta to the skillet as well. Toss everything together until the pasta is well coated in the luscious sauce. If the sauce seems too thick, add a splash or two of the reserved pasta water until it reaches your preferred consistency. Garnish with fresh parsley or green onions. Serve immediately and enjoy!