In a large bowl, combine the cumin, chili powder, smoked paprika, garlic powder, onion powder, salt, and black pepper. Rub the spice mixture all over the pork shoulder pieces.

Place the seasoned pork in the crockpot. Add the chopped onion, minced garlic, orange juice, and lime juice. Stir to combine.

Cover and cook on low for 8 hours or until the pork is tender and easily shredded.

Once cooked, remove the pork from the crockpot and shred it using two forks. Return the shredded pork to the crockpot and mix it with the juices.

Serve the carnitas in tacos, burritos, or over rice, garnished with fresh cilantro and lime wedges.