In a blender, combine achiote paste, orange juice, pineapple juice, garlic, cumin, oregano, salt, and black pepper. Blend until smooth.

Place the pork slices in a bowl and pour the marinade over them. Mix well and let marinate for at least 1 hour, preferably overnight in the refrigerator.

Preheat the grill to medium-high heat. Remove the pork from the marinade and discard the marinade.

Grill the pork slices for about 5-7 minutes on each side, or until cooked through and slightly charred.

Remove from the grill and let rest for a few minutes before slicing into small pieces.

Warm the corn tortillas on the grill for about 30 seconds on each side.

Place a portion of the grilled pork on each tortilla, top with diced pineapple, chopped onion, and cilantro.

Serve with lime wedges on the side.