Ingredients:

Al Pastor Marinade

• 3 dried ancho chiles, stemmed
• 3-6 dried chiles de árbol (depending on how spicy you want the al pastor), stemmed
• 3 garlic cloves, lightly crushed
• 1 cinnamon stick, broken into pieces
• 1/2 tsp. black peppercorns
• 1/2 tsp. cumin seeds
• 1 1/2 cups water
• 1/2 cup cider vinegar
• 4 tsp. light brown sugar
• 1 1/2 tsp. achiote paste
• 1 tsp. kosher salt
• 3/4 tsp. dried Mexican oregano

Chicken Skewers

• 2 pounds boneless, skinless chicken thighs, cut into 1-inch pieces
• 8 (10-inch) skewers (soaked in water if wooden)
• 1 1/2 tsp. kosher salt
• Fresh pineapple wedges (about 1 inch each) – 2 or 3 per skewer
• Canola oil, for grilling
• Warm corn tortillas, for serving

Method

1. Toast ancho chiles in a medium saucepan over medium-low, turning occasionally, until fragrant and pliable, about 5 minutes. Add chiles de árbol, garlic, cinnamon, peppercorns, and cumin seeds; cook, stirring constantly, until chiles de árbol just start to brown and spices are fragrant, about 1 minute. Add 1 1/2 cups water; bring to a boil over high. Boil 5 minutes, stirring and turning chiles occasionally. Remove from heat, and let the chile mixture stand for 20 minutes.
2. Transfer the chile mixture and cooking liquid to a blender; process until smooth, about a minute or more. Add vinegar, brown sugar, achiote paste, salt, and oregano; process until smooth, about 30 seconds.
3. Reserve 1/4 cup of al pastor marinade in a small bowl, and set aside. Place chicken and remaining marinade (about 1 1/2 cups) in a large ziplock plastic bag. Press out as much air as possible, and seal bag; shake bag to coat chicken evenly in marinade. Place the bag on a large plate or rimmed baking sheet, and refrigerate at least 30 minutes or up to 1 hour.
4. Preheat a grill to medium-high (400°F to 450°F). Remove chicken from marinade, and place on a large plate or rimmed baking sheet; discard bag with marinade. Thread evenly divided chicken pieces onto skewers along with pineapple chunks, pressing pieces together so that they are just touching; sprinkle with salt. 
5. Working in batches if necessary, place skewers on oiled grates, and grill, turning occasionally, until chicken is charred on all sides and cooked through, 12 to 15 minutes, brushing with reserved 1/4 cup marinade during final 3 minutes of grilling. Transfer skewers to a large platter. Serve hot with warm corn tortillas.