Make the sauce:

1. Combine all the sauce ingredients in a small saucepan and bring to a boil over medium-high heat, stirring often to prevent burning.
2. Reduce the heat and simmer gently for 5 minutes, stirring occasionally.  Add water as necessary to thin out the sauce if it’s too thick.  Remove from the heat and let cool to room temperature before using.  The sauce should keep for several weeks if tightly covered and refrigerated.

Pickle the vegetables:

1. In a medium bowl, whisk the vinegar, sugar, and salt until the sugar and salt is dissolved.  Add the carrots and cucumber to the bowl and toss to coat all the pieces with the pickling liquid.
2. Cover tightly and refrigerate for at least 30 minutes.  The pickled veggies can be made ahead of time.  They will keep for a few days if covered tightly and refrigerated.

Smoke the pork belly:

1. Set up your smoker for a 225°F cook.
2. Apply a thin coat of yellow mustard to the pork belly.  This helps the rub to stick.
3. Combine all the rub ingredients in a small bowl, breaking up any clumps with your hands.  You’ll have more rub than you need.  Store any extra rub in a tightly sealed container for up to 6 months.
4. Using a shaker or other device of your choosing, generously coat the pork belly in the rub.  Place the pork belly in the smoker, fat side up.
5. Smoke the pork belly, rotating as necessary for even cooking, until a temperature probe inserted into the thickest part of the belly reads about 200°F, about 6-8 hours.  The probe should also slide in very easily, as if the pork belly is a warm stick of butter.  Take it off the smoker and let rest for 30 minutes.

Make the gua bao:

1. Slice the pork belly crosswise into 1/2 inch thick slices.  Cut each slice into smaller pieces that will fit nicely into a gua bao bun.  Try to resist the temptation to eat all the pork belly yourself during this step.
2. (Optional step) Crisp up each slice in a cast iron pan over medium heat, until both sides are golden brown.  Remove the pork belly from the pan and set aside on a paper towel lined plate.  You’ll probably need to do this in batches unless you have multiple cast iron pans.
3. Working in batches, steam the buns according to the package directions. (see notes)
4. Toss the pieces of pork belly in a bowl with some of the asian barbecue sauce, reserving some sauce to spread on the buns.
5. Paint a little sauce on the inside of each bun, then add some of the pickled carrots and cucumbers.  Nestle a slice of pork belly into the bun and top with the cilantro and sliced chiles.