Preheat a smoker to 250°F. In a large bowl, combine the ground turkey, panko, egg, diced onion, 2 tablespoons of the barbecue sauce, smoked paprika, garlic powder, salt, and black pepper. Mix gently until just combined.
Shape the mixture into a compact loaf and place it on a foil-lined baking sheet. Brush the top and sides with half of the remaining barbecue sauce.
Smoke the meatloaf until its center reaches 165°F, brushing it with the rest of the barbecue sauce during the final 15 minutes. Let it rest for 10 minutes so it holds together when sliced.
Toast the hamburger buns in the smoker for a few minutes, cut sides up, until lightly crisp. Slice the meatloaf into four portions.
Place a slice of meatloaf on each bun bottom. Top with coleslaw and pickled jalapeños, then close with the bun tops and serve.