- 1
**Toast and rehydrate the chiles:** In a dry skillet over medium heat, toast guajillo and ancho chiles 30–45 seconds per side until fragrant. Transfer to a bowl, cover with boiling water, and soak 15 minutes until softened.
- 2
**Make the marinade:** Drain chiles and blend with achiote paste, garlic, orange juice, vinegar, oregano, cumin, salt, and pepper until very smooth, about 2 minutes. Strain through a medium sieve.
- 3
**Marinate the pork:** Coat the pork slices thoroughly in the marinade. Refrigerate at least 4 hours, preferably overnight.
- 4
**Make the pineapple topping:** Toss diced pineapple with guajillo powder and a pinch of salt. Set aside at room temperature.
- 5
**Cook the pork:** Heat a cast-iron skillet or grill pan over high heat until very hot. Working in batches to avoid crowding, sear pork slices 2–3 minutes per side until deeply caramelized with charred edges. Let rest 2 minutes, then roughly chop or slice into bite-sized pieces.
- 6
**Warm the tortillas:** Char each tortilla directly over a gas burner flame for 15–20 seconds per side, or in a dry skillet. Keep warm in a folded towel.
- 7
**Build the tacos:** Double up two tortillas per taco. Add a generous spoonful of al pastor, a pinch of diced white onion, a few cilantro leaves, and a spoonful of pineapple topping.
- 8
**Finish and serve:** Add a drizzle of salsa and a squeeze of fresh lime over each taco. Serve immediately.