There, in true al pastor form, the taqueras marinate thin, thin slices of pork shoulder in a mixture of chilies and aromatics colored bright red with achiote. The slices are then stacked onto a vertical skewer, forming a large, bell-shaped trompo (spinning top), which gets topped with an onion and pineapple, and slowly rotates in front of a vertical grill. If there's a reason it resembles shawarma or doner kebab, it's because the concept was first introduced to Mexico by Lebanese immigrants.