Inspect each breast and trim off any skin or fat. Using fresh water thoroughly wash each chicken breast. Pat dry with paper towel and place in a large ziplock bag. (If you don't have a large ziplock bag you can do the next few steps in batches or by using a bowl).
Pour your marinade in the ziplock bag and shut securely. Massage the marinade over the breasts to coat well. Make sure each breast is coated well as this will help them stay tender and juicy while cooking.
Place the chicken breasts in the refrigerator t marinade for at least 1 hour. You can prepare and marinade over night if you want more flavor.
When you are ready to cook preheat your smoker to 250ºF following your smokers instructions.
While your smoker is coming to temperature individually wrap each chicken breast in foil.
Once your smoker has got to temprature, add the hickory chunks to the smoker box and wait until you get a good smoke.
Once you have got a good smoke, add the foil parcels to the smoker, close and leave for around 2 - 2 ½ hours. (no peeking!)
After 2 - 2 ½ hours check the internal temprature of the chicken breast, you are looking for 160ºF.
Once cooked let rest for 10 minutes then slice & serve.