Preheat smoker to 300 degrees.
Season chicken liberally with desired seasoning mix.
Place chicken on smoker, away from the heat source.
For the sauce, combine tomato sauce, chipotle chiles, garlic cloves, white onion, cilantro, salt, pepper, cumin, and lime juice in a blender. Blend until smooth.
Place sauce in a deep sided skillet, directly over heat source of pellet smoker (if possible).
Once the internal temperature of the chicken is around 130-140 degrees, place the breasts into the sauce to finish cooking. Move sauce pan away from heat source for a gentler cook for the remaining time.
When the chicken has reached an internal temperature of 160 degrees, remove from the smoker and allow to rest for 10-15 minutes at room temperature.
After the chicken has had time to cool slightly, shred the meat with two forks and mix thoroughly into the sauce.
Serve on rice or tortillas, with a bit of cotija cheese and a little fresh cilantro.