In a large bowl, combine pork chunks with chili powder, cumin, oregano, orange juice, lime juice, oil, garlic, salt, and pepper. Toss to coat evenly and refrigerate for 30 minutes.
Heat a large skillet over medium-high heat. Add marinated pork and sear until browned on all sides, about 2-3 minutes per side.
Add quartered onion and bay leaves to the skillet. Reduce heat to low, cover, and simmer for 1.5-2 hours until pork is fork-tender.
Increase heat to medium and cook uncovered until liquid evaporates and pork begins to crisp in its rendered fat, about 10-15 minutes.
Remove from heat and shred the pork using two forks. Discard bay leaves.
Preheat oven to 375°F (190°C).
Spread tortilla chips evenly on a large baking sheet or oven-safe platter.
Distribute shredded carnitas over the chips, then sprinkle with both cheeses.
Bake for 5-7 minutes until cheese is completely melted and bubbling.
Top with diced red onion, jalapeño slices, avocado, cilantro, and dollops of sour cream.
Serve immediately with lime wedges and pico de gallo on the side.
Notes
For extra crispy nachos, pre-bake the tortilla chips for 5 minutes before adding toppings.
Leftover carnitas can be stored in the refrigerator for up to 4 days or frozen for 3 months.
For a make-ahead option, prepare the carnitas a day in advance and assemble nachos just before serving.
Use thick, restaurant-style tortilla chips that can support the weight of the toppings.
Nutrition facts are estimates and may vary based on ingredients used, portion sizes, and preparation methods.