Tacos al Pastor

Stem and seed all of the dried chiles and place them in a microwave-safe bowl. Cover with water and microwave at high power until softened, about 3 minutes. Let cool slightly, then drain and transfer to a blender. Add the orange juice, lime juice, soda and vinegar. In a spice grinder, grind the annatto with the oregano, cumin, clove, sugar and garlic powder until fine. Add the spice mixture to the blender and blend until smooth.

Transfer the marinade to a saucepan. Add the 2 tablespoons of oil and cook over moderate heat, stirring constantly, until very thick, about 5 minutes; let cool. Transfer the marinade to a large resealable plastic bag. Add the pork and onion and seal the bag. Refrigerate overnight.

Light a grill. Remove the pork and onion from the marinade and scrape most of it off. Brush the pork and onion with oil and season with salt and pepper. Grill over moderate heat, turning, until the meat is cooked through, 15 minutes. Transfer the pork and onion to a work surface, cover loosely with foil and let stand 10 minutes.

Cut the pork into strips. Serve the pork and onion with the warmed tortillas, grilled pineapple, red onion and cilantro.