In a medium saucepan, combine the apple cider vinegar, ketchup, yellow mustard, brown sugar, molasses, hot sauce, black pepper, and salt.
Bring the mixture to a simmer over medium heat, stirring occasionally.
Cook for 5 minutes to allow the flavors to meld together.
Carefully transfer 1 cup (240 ml) of the finished sauce to a separate bowl and set it aside for serving later.
Add the sliced seitan to the saucepan with the remaining sauce.
Continue to cook for 10 minutes, stirring periodically, until the seitan is heated through and has absorbed the sauce.
To assemble, divide the saucy seitan mixture evenly among the four hamburger buns.
Serve immediately, topped with pickle chips and a side of coleslaw. Offer the reserved sauce for drizzling.