Season the chicken breasts with salt and pepper.
Place the chicken in the bottom of the crockpot.
Mix the cream of chicken soup, ranch dressing mix, and chicken broth in a bowl.
Pour the mixture over the chicken.
Add onions and mushrooms if using.
Cover and cook on low for 6 to 8 hours.
Shred the chicken with two forks.
Stir the shredded chicken back into the gravy.
Serve over rice or mashed potatoes.
Garnish with chopped parsley if desired.