In a medium-sized saucepan, boil water and salt it. Add your pasta, and cook according to the package instructions until al dente. When the pasta is cooked, reserve ½ cup of the pasta water and drain the pasta.
Meanwhile, season and cook the chicken. Season the chicken cutlets with salt, pepper, and 1 tablespoon of cajun seasoning.
Heat olive oil and melt 1 tbsp of butter in a skillet, add the seasoned chicken cutlets and cook for 3-4 minutes per side until they are cooked through. Remove from the pan. Cover to keep warm. Cook the chicken in batches as needed so that the pieces have enough room in the pan to brown.
If there are any burnt seasonings left in the pan, wipe them away with paper towels. You can add water to make this easier.
Melt the remaining tablespoon of butter, and saute the onion until soft and translucent. Add garlic, and saute for 30 seconds then add the diced tomatoes. Stir in the remaining cajun seasoning and heavy cream.
Use a flexible spatula or a whisk to mix everything together. Then add the parmesan cheese and let it melt into the sauce. Season with salt and pepper, tasting and adjusting as needed. If the sauce seems too thick at any point, stir in some of the pasta water that you saved earlier.
Slice the cooked chicken into thin strips, then mix it in with the pasta and sauce. Serve, garnished with chopped parsley and extra grated parmesan cheese.