Combine the dried spices in a small bowl.
Chop the onion and place it in the bottom of the slow cooker. Rinse the chicken (remove neck and giblets) then rub the spice mixture all over chicken (placing some under the skin and in the cavity). Put prepared chicken on top of the onions in the slow cooker, place lid on and turn it on high. There is no need to add any liquid. Cook for 4-5 hours (for a 3 to 5 pounds chicken) or until the chicken is falling off the bone.