Flour tortilla quesadillas filled with al pastor pork and melted cheese are a taquería favorite. This high protein, family-friendly dish is a fresh, cheesy twist on classic tacos al pastor.
In a large mixing bowl, combine achiote paste, apple cider vinegar, orange juice, oregano, cumin, minced garlic, salt, and black pepper to make a marinade.
Add thinly sliced pork shoulder to the marinade, tossing well to coat. Cover and refrigerate for at least 1 hour (up to overnight for best flavor infusion).
Heat a large skillet or grill pan over medium-high heat. Add vegetable oil and cook the marinated pork slices in batches, searing until just cooked through and slightly caramelized, about 3–4 minutes per side. Transfer to a plate and let rest briefly.
Wipe out the skillet and lower the heat to medium. Place a flour tortilla in the pan, sprinkle with ½ cup Monterey Jack cheese, layer with a quarter of the pork, pineapple, onion, and cilantro, then top with another tortilla.
Cook each gringa for 3–4 minutes per side, pressing gently, until the tortillas are golden brown and cheese is fully melted. Slice into wedges and serve immediately.