The El Pollo Loco workers appear in the Season Fifteen episode "The Last of the Meheecans".
Background[]
When Butters (dressed up as "Mantequilla") is dropped off to El Pollo Loco by Mr. and Mrs. Whipple, he is taken into the restaurant by the workers. Upon hearing that Butters is "Mantequilla", the workers recognize him from posters which the boys had erected. They then begin to question their place in the United States, misinterpreting Butters' desire to "cross the border", which ultimately led them to their decision to return to Mexico.
Along with Mantequilla, the workers make their way to a nearby hospital, rallying other Mexican workers to return to Mexico as well.