Mix together the bbq sauce, taco seasoning and chipotle. Add the chicken to a slow cooker. Slice half the onion and add the slices to the chicken, then sprinkle with the salt.
Pour bbq sauce mixture over the chicken, cover and cook on high for 4 hours, or low for 6 hours. Remove chicken from the slow cooker and sauce and shred with two forks. Return shredded chicken to the sauce.
Prepare the monster eyes by slicing the string cheese in rounds and cutting the black olives with a small and bubble tea (large) straw for little circles. Or cut small triangles with a paring knife for the scary eyes. Slice baby cucumbers for the cyclops eyes. Cut slits in the top of the rolls to insert eyes so they stand up.
Fill the rolls with chicken, top with guacamole and top with the remaining chopped red onion and cilantro. Serve warm or room temperature.
Extra chicken can be kept airtight in the fridge for up to a week.