In a medium bowl, combine minced garlic, ground cumin, dried oregano, smoked paprika, black pepper, and salt. Pour in orange juice and lime juice. Add olive oil, mixing until well combined to create a marinade.

Place pork shoulder into your slow cooker. Pour the prepared marinade evenly over the pork, ensuring every inch is generously coated. Let marinate for at least 30 minutes or overnight in the refrigerator.

Slice onion and scatter the slices around and on top of the marinated pork in the slow cooker.

Cover the slow cooker with its lid and set to cook on low for 8 to 10 hours or on high for 4 to 5 hours.

Once cooked, carefully remove the pork from the slow cooker and place it on a cutting board. Shred the pork into bite-sized pieces, discarding excess fat if desired.

Return the shredded pork to the slow cooker, mixing it with the cooking juices. Allow to meld for a few minutes. Serve garnished with fresh cilantro alongside rice and black beans.