In a large pot of salted boiling water, cook the fettuccine according to package instructions until al dente. Reserve 1/2 cup of the pasta water, then drain and set aside.
In a bowl, toss the sliced chicken breasts with 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, or until cooked through and golden brown. Remove the chicken from the skillet and set aside.
In the same skillet, add the diced onion and sliced bell pepper. Sauté for about 3-4 minutes until the vegetables start to soften. Add the minced garlic and cherry tomatoes, cooking for an additional 2 minutes until fragrant.
Pour in the heavy cream and stir to combine with the vegetables. Bring the mixture to a simmer, then add the cooked chicken back to the skillet. Stir in Parmesan cheese, and adjust the seasoning with salt and pepper. If the sauce is too thick, add the reserved pasta water a little at a time to reach desired consistency.
Add the cooked fettuccine to the skillet and toss everything together so that the pasta is fully coated in the sauce.
Serve the pasta in bowls, garnished with freshly chopped parsley for a pop of color.
Notes
Adjust the spice level by varying the amount of Cajun seasoning.