Place first 8 ingredients (garlic through lemon zest) in a large crock cooker; stir well to combine.
Cover and cook on LOW for 4 to 6 hours or until chicken is very tender and cooked through.
Stir in pecans and lemon juice to the crock cooker then, using a slotted spoon, scoop chicken mixture into lettuce leaves and serve.
*Partially frozen chicken is easier to chop.