Preheat oven to 420℉ and line a baking sheet with parchment paper.
Make BBQ sauce: in a small bowl, mix together ketchup, apple cider vinegar, maple syrup, coconut aminos, mustard, paprika, garlic powder, and black pepper. Set aside.
Next, shred mushrooms either by using two forks or your hands. I like to break the mushrooms in half with my hands first to create rugged and uneven ends for easier shredding. Transfer mushrooms to a mixing bowl.
Drizzle the avocado oil along with most of the BBQ sauce on the mushrooms, then toss to coat well. Transfer to a lined baking sheet. Arrange in one layer and give enough space between each piece to crisp up.
Place in the oven and bake for 20-25 minutes, tossing halfway through, until the mushrooms are tender and the edges start to get crispy.
Cut hamburger buns in half and spread vegan butter on the cut side. Toast on a skillet over medium heat until golden or place under the broiler for about 1 minute.
Divide the pulled BBQ mushrooms on toasted buns, top with the rest of the BBQ sauce and some coleslaw. Close your sandwich and enjoy!