If using dried beans, prepare according to package directions. Set aside 2 cups cooked beans for this recipe, and save the rest for another use. (One cup dried beans will yield 3 cups cooked.)
Drain and rinse jackfruit, then drain again. Pat dry using paper towels. Using your fingers, pull jackfruit apart so that it looks shredded.
In a large skillet, combine onion, garlic, chili powder, paprika, vinegar, and 1/3 cup water. Bring to a boil over high heat, then reduce to a simmer. Let cook until onions are soft and translucent and water has evaporated, 5–7 minutes.
Stir in jackfruit, beans, barbecue sauce, and 1/3 cup water. Let simmer, stirring frequently, until flavors marry and jackfruit is soft, for 25 minutes. Add an additional 1–2 tablespoons water if pan gets too dry. Remove from heat. If necessary, use 2 forks to break apart any large chunks of jackfruit.
Season with cilantro and/or hot sauce (if using).
To serve, place lettuce leaves, tomato slices, and thinly sliced red onion on the bottom half of each sandwich thin “bun.” Add 1/2 cup jackfruit barbecue for each sandwich, and top with remaining bun. Serve.