The night before, butterfly the pork (or have your butcher do it): Butterflying means to cut the meat open so that it lays in a flat even thickness. Cut through the thick part of the meat, horizontally to almost the edge. Unfold it to get a broad flap of meat, about 1 1/2 - 2 inches thick.
Place pork on a baking sheet and liberally spread the Stubb's Pork Spice Rub over both sides of the flesh, massaging it in with your hands. Cover with plastic wrap and refrigerate overnight.
The next day, soak the wood chips in a bowl filled with water for an hour.
for the pickled onions
Combine the vinegar, sugar and kosher salt in a measuring cup. Stir until sugar and salt have dissolved. Place the onions in a small bowl and cover with the vinegar mixture. Set aside for at least an hour and up to 2-3. (note: pickled onions will last a week or so in the fridge and they're great on sandwiches or with barbecued chicken, fish and seafood.)
for the barbecue sauce
In a small saucepan, combine Stubb's Spicy Bar-B-Q Sauce, Stubb's Sticky Sweet Bar-B-Q Sauce, pineapple juice and worchestershire sauce. Heat to boiling and reduce heat to a simmer. Cook, uncovered until sauce reduces and thickens, about 15 minutes.
ready the grill
Add the chips to the smoker box and place over one of the burners. Preheat your gas grill with a closed lid and wait for a soft white smoke to begin emanating from the grill (about 10-15 minutes).
Turn off all the burners except the one directly under the smoker box, for indirect cooking. Then place the pork opposite the smoker box, so it's not getting direct heat. Cook for about an hour at 350 degrees, without opening the lid.
After an hour, use the meat thermometer to check the temperature of the meat by inserting it into the thickest portion. When it reaches 125 degrees, turn the rest of the burners on and use direct heat for the remainder of the cooking. Grill the pork, watching for flare ups and turning the meat once or twice while cooking. You want to achieve an internal temperature of 165 degrees before pulling it off the grill.
During the last 15 minutes of cooking, liberally brush the barbecue sauce over the meat. Cook for 5 or so minutes, then flip the meat and brush sauce on the other side. Cook for 5 minutes and flip again, so the sauce forms a nice crust on the meat.
When the pork reaches 165 degrees, transfer it to a cutting board and tent with tin foil. Let the meat rest for 15 minutes so the juices can redistribute throughout the flesh.
for the pineapple
Meanwhile, grill the pineapple rings until you get some nice grill marks, flipping halfway through -- about 5-8 minutes. Transfer to a platter.
for the sandwiches
Using a very sharp knife, slice the pork as thinly as possible across the grain.
Place a pineapple ring on the bottom of a bun and top with a generous serving of sliced pork, followed by extra barbecue sauce, pickled onions and fresh cilantro leaves.