The combination of earthy dried chiles and fruity pineapple are hallmarks of al Pastore. But so are long marination times and slow roasting. These speedy tacos are far from al Pastore, but they do bring together the similar citrusy, fruity and earthy flavors. Make sure your grill is hot and well greased to get the right char and caramelization on the pork.
Preheat a grill to medium high. Put the chiles on a microwave-safe plate and microwave until fragrant and pliable, about 10 seconds (or toast in a small dry skillet over medium heat). Remove the stems, then tear the chiles and transfer to a blender. Add the vegetable oil, 1 pineapple slice, the orange juice, 1/2 teaspoon salt and a few grinds of pepper. Puree until smooth.
Trim the pork, then halve crosswise and lengthwise to create 4 pieces. Put in a shallow dish, add the chile puree and turn to coat; let marinate, 10 to 15 minutes.
Meanwhile, put the onion in a fine-mesh sieve and rinse under cold water; transfer to a bowl. Stir in the lime juice and a big pinch each of salt and pepper; set aside.
Remove the pork from the marinade and season with salt and pepper. Oil the grill grates, then transfer the pork and remaining 2 pineapple slices to the grill. Cover the grill and cook, turning the pineapple and pork occasionally, until the pineapple is well marked, about 4 minutes, and the pork is just cooked through and lightly charred, 8 to 10 minutes.
Chop the pineapple and add to the onion mixture along with the chopped cilantro; season with salt and pepper. Slice the pork and the avocado. Warm the tortillas as the label directs. Fill with the pork, pineapple mixture, avocado and cilantro leaves.