Place the pork tenderloin in a slow cooker and rub all sides with the dried oregano, ground cumin, garlic powder, sea salt, and black pepper.
Pour the fresh orange juice and lime juice over the seasoned pork.
Cover and cook on low for 6 to 8 hours (or high for 3 to 4 hours) until the pork is tender enough to shred easily with a fork.
Remove the pork from the slow cooker and transfer to a cutting board; shred the meat using two forks.
Optional: For crispy edges, place the shredded pork in a non-stick skillet over medium-high heat for 3-5 minutes until golden brown.
Warm the corn tortillas in a dry skillet over medium heat for 30 seconds per side until they are charred and pliable.
Divide the shredded pork evenly between the two tortillas.
Top the tacos with sliced avocado, diced red onion, and freshly chopped cilantro.
Serve immediately with a lime wedge on the side for a final squeeze of brightness.