Place the chicken breasts in the bottom of a 6-quart slow cooker.
Season the chicken generously with salt, pepper, poultry seasoning, and garlic powder.
Top the seasoned chicken with the cream of chicken soup, cubed butter, Better Than Bouillon base, and chicken broth. Do not stir.
Cover and cook on LOW for 4 to 6 hours. The chicken should be fully cooked and tender enough to shred.
Remove the chicken from the pot and shred it using two forks. Return the shredded meat to the slow cooker.
Stir in the frozen egg noodles (and frozen mixed vegetables if using).
Switch the slow cooker to HIGH heat, cover, and cook for an additional 60 to 90 minutes. Stir occasionally to ensure noodles do not stick together.
Check that noodles are tender and the broth has thickened to a stew-like consistency.
Serve warm, garnished with fresh parsley if desired.