In the Crockpot, place the boneless, skinless chicken breasts at the bottom.
Sprinkle the ranch dressing mix evenly over the chicken.
In a medium bowl, combine the cream of chicken soup, chicken broth, and brown gravy mix. Stir until well blended.
Pour the gravy mixture over the chicken in the Crockpot.
Add the diced onion on top of the mixture.
Season with salt and pepper to taste.
Cover the Crockpot and cook on low for 6 hours or until the chicken is tender and cooked through.
After cooking, shred the chicken using two forks and mix it with the gravy.
Serve hot over rice or mashed potatoes, and garnish with fresh parsley if desired.