Prepare the marinade: In a blender, combine achiote paste, guajillo chili powder, cumin, oregano, garlic, vinegar, orange juice, and salt. Blend until smooth.

Marinate the pork: Place the thinly sliced pork in a large bowl. Pour the marinade over the pork, ensuring all pieces are well coated. Cover and refrigerate for at least 2 hours, preferably overnight.

Cook the pork: Heat a large skillet or grill over medium-high heat. Cook the marinated pork slices for about 3-4 minutes per side until fully cooked and slightly charred.

Prepare the pineapple: In the same skillet, cook the diced pineapple for 2-3 minutes until slightly caramelized. Set aside.

Warm the tortillas: Heat the corn tortillas on a dry skillet or over an open flame for about 30 seconds per side until warm and pliable.

Assemble the tacos: Place a few slices of cooked pork on each tortilla. Top with caramelized pineapple, chopped onion, and fresh cilantro. Serve with lime wedges on the side.