Preheat your smoker to 225°F using fruitwood or a mild hardwood like apple or cherry.
In a large bowl, toss the pork belly cubes with the oil.
In a separate bowl, mix together the brown sugar, smoked paprika, onion powder, garlic powder, salt, pepper, and ground mustard. Sprinkle the seasoning over the pork and toss to coat evenly.
Arrange the pork belly cubes directly on the smoker grates, leaving space between each piece. Smoke for 2 hours, or until the pork has a dark, tacky bark and starts to render.
Transfer the pork belly to a foil tray or disposable aluminum pan. Add the BBQ sauce, honey, brown sugar, and butter right on top of the pork — do not mix.
Cover the tray tightly with foil, then return it to the smoker. Cook for another 30–45 minutes, or until the sauce is bubbling and the pork is tender.
Uncover the tray and stir everything together. Let rest for 5 minutes before serving.