Heat the olive oil in a skillet over medium heat. Add the diced bell pepper and onion and cook for 5 to 7 minutes, stirring occasionally, until softened. Set them aside to cool.

Preheat a smoker to 250°F. In a large bowl, combine the ground beef, breadcrumbs, egg, milk, Worcestershire sauce, garlic powder, salt, black pepper, and cooled peppers and onions. Mix gently until just combined.

Shape half of the meat mixture into a compact loaf on a sheet of foil or a small smoker-safe pan. Lay 2 slices of provolone over the center, leaving a little space around the edges. Cover with the remaining meat mixture and seal the edges so the cheese is enclosed.

Place the loaf in the smoker and cook until the center reaches 150°F, about 1½ to 2 hours. Check the temperature in the center of the meat, taking care not to touch the cheese pocket.

Stir the barbecue sauce and brown sugar together in a small bowl. Brush the mixture over the meatloaf, then continue smoking until the center reaches 160°F.

Lay the remaining 2 slices of provolone on top. Close the smoker for a few minutes, just until the cheese melts. Rest the meatloaf for 10 minutes before slicing so the filling stays in place.