In a medium pot, add the guajillo chiles, ancho chiles, and enough water to completely cover them. Bring to a boil over high heat. Remove the pot from the heat, cover it, and let the chiles soak for 10 minutes to soften.
Using a slotted spoon, transfer the softened chiles to a blender. Add 1 cup of the chile-soaked water, 1 cup of diced pineapple, the achiote paste, onion, garlic, chipotle pepper in adobo sauce, salt, Mexican oregano, cumin, and white vinegar. Blend for 3 to 5 minutes until completely smooth.
Combine the pork shoulder with the marinade in a large glass or stainless steel bowl. Toss together until all the meat is fully coated, then cover and refrigerate for 4 to 24 hours.
Preheat a grill for direct heat grilling at high heat (450-500°F) or a grill pan over high heat. Remove the pork shoulder from the marinade and shake off any excess marinade. Grill for 3-4 minutes per side. Transfer to a large plate and set aside to rest for 5 minutes.
While the meat is resting, brush oil on all sides of the remaining pineapple slices. Grill over high heat until heated through and grill marks appear. Transfer to a cutting board and dice.
Chop the grilled meat into small bite-sized pieces and serve in warm corn tortillas topped with the diced grilled pineapple, diced white onion, chopped cilantro, a squeeze of fresh lime juice, and salsa verde. Slice thinly against the grain and serve.
Notes
Cooking indoors: You can make this recipe on your stovetop in a large, heavy skillet or grill pan over medium-high heat. The flavor won’t be exactly the same, but it will still be delicious!