Load the base: Add chicken breasts to the slow cooker.
Pour in Alfredo sauce, chicken broth, and heavy cream. Stir in garlic, Italian seasoning, onion powder, salt, and pepper. Dot with butter if using.
Cook low and slow: Cover and cook on Low for 4–5 hours or High for 2.5–3 hours, until the chicken is tender and easily shreds.
Shred the chicken: Remove chicken to a cutting board and shred with two forks, or cube it if you prefer.
Return it to the slow cooker and stir.
Add pasta: Stir in the uncooked pasta, making sure it’s submerged in the sauce. Cover and cook on High for 20–35 minutes, stirring once halfway, until pasta is al dente. Timing depends on pasta shape and your slow cooker.
Finish the sauce: Stir in the Parmesan cheese until melted and smooth.
If adding spinach or other add-ins, stir them in now. If sauce seems thick, add a splash of warm broth or milk. If thin, let it sit uncovered for 5–10 minutes to thicken.
Serve: Taste and adjust seasoning.
Spoon into bowls, top with extra Parmesan and parsley, and serve warm.