Step 1
Place pork in a large brining vessel. Cut a few slashes into the fat side of the pork.
Step 2
Whisk salt pineapple juice and water together in a large bowl. Pour brine over the pork. Refrigerate for 12 to 24 hours.
Step 3
Combine salt ancho powder chipotle powder garlic powder cumin cinnamon and oregano together for the rub.
Step 4
Remove pork from the brine and place on a deep baking pan lined with foil. Season generously with the spice rub. Reserve remaining spice rub for another use.
Step 5
Preheat a charcoal grill for 300 to 325 degrees F (150 to 175 degrees C). Place 2 bricks on the grate if you like and place the baking pan on top.
Step 6
Grill occasionally spooning rendered juices over the meat until very tender about 7 hours. Make sure to maintain the same 25-degree range in temperature by adjusting the vents under and on top of the grill or smoker. An instant-read thermometer inserted into the center of the pork should read 195 degrees F (91 degrees C).
Step 7
Remove pan from the grill wrap top in foil and let rest for 1 hour. Meanwhile cook pineapple over the last of the coals until nicely charred 7 to 10 minutes.
Step 8
Dice the grilled pineapple to get about 2 cups. Combine in a bowl with serrano pepper red peppers cilantro and rice vinegar. Season with salt and a pinch of the leftover spice rub.
Step 9
Remove pork bone and pull the meat apart. Add to a bowl with some of the rendered fat; pull apart with 2 forks. Place some pork over each bottom bun top with pineapple salsa and cover with the other bun half.