Rub the chicken breasts with Cajun seasoning, garlic powder, paprika, salt, and pepper. Marinate for 15-20 minutes if possible.
Place the seasoned chicken in the slow cooker. Add sliced bell peppers and onion, then pour in the chicken broth. Set to low for 6–7 hours or high for 3–4 hours.
Remove the chicken from the slow cooker and shred it with two forks. Return the shredded chicken to the slow cooker and stir.
Add cream cheese and shredded Parmesan cheese to the slow cooker. Stir until melted and cook on low for an additional 10-15 minutes.
Cook the pasta according to package directions until al dente. Drain well before adding to the slow cooker.
Stir the cooked pasta into the slow cooker mixture until coated in the sauce.
Serve the dish in bowls or plates, garnished with parsley, extra Parmesan, and crushed red pepper flakes if desired.