Cut Jackfruit: Slice off the center core portion of the jackfruit. Use your hands to roughly shred the jackfruit chunks. Set aside.
Sauce: In a medium bowl, whisk the ketchup, apple cider vinegar, lemon juice, maple syrup, mustard, and vegan Worcestershire sauce until combined. Set aside.
Cook Jackfruit: Heat the oil in a large non-stick skillet over medium-high heat. Cook the jackfruit for about 7 minutes, or until golden brown, while using the side of a spatula to shred the pieces. Add the smoked paprika, onion powder, garlic powder, chili powder, and black pepper. Cook for 1 minute, stirring constantly. (See recipe notes for oil-free.)
Combine: Add one-half of the prepared BBQ sauce, the red onions, and ¼ cup water. Bring the sauce to a gentle boil. Reduce the heat and simmer covered for about 20 minutes, or until the jackfruit is tender and the sauce has thickened. Stir occasionally, adding more sauce or water as desired.
Optional: Meanwhile, toast the buns and prepared the mashed avocado. In a medium bowl, mix the avocado, lemon juice, salt and black pepper. Spread the mashed avocado onto one side of the buns. Top with the desired amount of BBQ pulled jackfruit.