In a slow cooker, combine chicken, cream, broth, and butter. Add Cajun seasoning, paprika, onion powder, and garlic powder; season with salt and pepper and toss to combine.
Cover and cook on High for 2 hours, or until an instant-read thermometer inserted into thickest part of chicken registers 165°.
Transfer chicken to a cutting board and let cool for 10 minutes. Thinly slice chicken.
Add sausage, penne, and Parmesan to slow cooker. Cover and continue to cook on High until penne is tender, 25 to 30 minutes more.
Add scallions and tomatoes and stir to combine; season with salt and pepper, if needed.
Return chicken to slow cooker. Top with parsley and more Parmesan.