Fill a large bowl with hot water and submerge the guajilo and ancho chiles in the water to rehydrate them. Let them rest in the water for approximately 10 minutes. Remove from water, pat dry and remove the stems and seeds.

Add the pork pieces to the bowl of a slow cooker.

Puree guajilo chiles, ancho chiles, 1/2 of the pineapple chunks, 1/2 of the red onion, adobo sauce, chipotle in adobo, garlic, lime juice, salt, oregano, cumin, black pepper, red pepper flakes and bacon grease until well-combined. Pour the sauce over the pork in the slow cooker and stir to coat.

Cook on medium for 8 to 10 hours or on high for approximately 5 to 6 hours. Remove the lid and using two forks, shred the meat. Be sure to stir it up with the sauce to get all that flavor!

In a medium bowl, combine the remaining pineapple and red onion to create a quick pineapple salsa.

Warm corn tortillas in the microwave between two damp paper towels for approximately 2 to 3 minutes. Fill the tacos with al pastor pork. Top with pineapple salsa, queso fresco and tomato. Serve with lime wedges.