Trim excess fat from the pork shoulder and cut into large chunks.
Place the pork in a slow cooker and add the orange juice, lime juice, minced garlic, cumin, oregano, sea salt, and black pepper.
Cover and cook on low for 6-8 hours or on high for 4 hours until the meat is fork-tender.
Once cooked, remove the pork and shred it using two forks.
Heat a non-stick skillet over medium-high heat and add the shredded pork with a splash of the cooking liquid, searing until the edges are golden and crispy.
Warm the corn tortillas in a dry pan or over an open flame for 30 seconds per side.
In a small bowl, mix the Greek yogurt with a squeeze of lime juice if desired to create a high-protein crema.
Assemble the tacos by dividing the crispy pork between the tortillas.
Top with diced red onion, fresh cilantro, and a dollop of the yogurt crema.