Season the chicken breasts and thighs with the salt, black pepper and onion powder.
Put the onion, garlic and bay leaf in a 6-quart slow cooker and arrange the chicken over them.
Pour in the broth, cover and cook on low until both cuts reach at least 165°F, 4 to 4 1/2 hours.
Transfer the chicken to a rimmed pan and discard the bay leaf.
Shred the meat into thick strands and strain and skim the cooking broth.
Fold 3/4 cup broth into the chicken, cool promptly and divide into covered meal-size portions.