Load the crockpot: Place chicken in the slow cooker. Sprinkle with Italian dressing mix, garlic powder, onion powder, black pepper, and red pepper flakes if using.
Add liquids: Pour in diced tomatoes with their juices and chicken broth.
Stir around the sides a bit to combine without fully covering the chicken in dry mix clumps.
Cook low and slow: Cover and cook on Low for 4–6 hours or High for 2.5–3.5 hours, until the chicken shreds easily.
Add creaminess: In the last 30 minutes, add the cream cheese cubes. Cover and let them melt. Stir gently until smooth.
Shred the chicken: Remove chicken to a plate, shred with two forks, and return it to the crockpot.
Stir to coat in the creamy sauce.
Cook the pasta: Boil pasta in salted water until al dente according to package directions. Drain, reserving 1/2 cup of pasta water.
Combine: Stir the Parmesan and butter into the crockpot sauce. Add cooked pasta and toss until every piece is coated.
If needed, splash in reserved pasta water to loosen the sauce.
Taste and finish: Adjust salt and pepper. Top with fresh herbs and extra Parmesan. Serve hot.