Season the cubed pork with seasoned salt. Heat the oil in a large skillet over medium-high heat and brown pork, in batches, on all sides. Transfer the pork to a large slow cooker and sprinkle with chili powder, cumin, oregano, garlic salt and pepper; stir well to coat. Top with onion quarters, orange juice and zest, lime juice and zest and garlic cloves. Cover and cook on low heat for 6 to 7 hours or on high heat for 4 to 5 hours, or until meat is very tender and falling apart.
Remove pork from the cooker using a slotted spoon; discard garlic and onion. Using two forks, shred pork into bite-size chunks. Skim excess fat from the cooking liquid, then return the shredded pork to the liquid. Fold gently to incorporate. Meanwhile, stir together all pico de gallo ingredients and season to taste.
Preheat the broiler to high; coat a baking sheet with nonstick spray. Spread the meat in a single layer on the baking sheet and broil until meat is lightly caramelized, 2 to 4 minutes.
Serve carnitas in Bibb lettuce cups, radicchio leaves or with flour or corn tortillas topped with pico de gallo and sprinkled with chopped fresh cilantro.