In a bowl, mix the vegetable oil, ketchup, smoked paprika, chili flakes, chipotle paste, vinegar, salt and pepper.
Remove the stems from the mushrooms and place on a baking tray then cover with the barbecue sauce. Cook for 20 to 25 minutes, then remove from the oven and allow to cool. Using 2 forks, shred the mushrooms, separating larger pieces with your fingers if needed.
For the slaw, mix together all the ingredients in a bowl.
Pile the mushroom mixture between the buns and top with the slaw. Serve with fries and more mayo.