Pat the chicken dry and combine the salt, paprika, cumin, ancho chile powder and garlic powder.
Rub the seasoning inside and over the chicken.
Spread the onion and tomatoes in a 6-quart slow cooker, add the broth and set the chicken breast-side up on top.
Cover and cook on low until the breast reaches 165°F and the thigh reaches 175°F, 5 to 5 1/2 hours.
Transfer the bird to a rimmed pan, remove the skin and bones and shred the meat into thick pieces.
Skim the cooker liquid and fold enough of the onion, tomato and juices into the meat to moisten it.
Serve the chicken in warm corn tortillas with shredded cabbage.