Cut the tempeh block in half crosswise, so you are left with 2 squares of tempeh.
Place in a medium skillet and cover with ½ cup (120ml) of water. Cover and steam over medium low heat for 15 minutes or until water is all gone.
Meanwhile, prepare the "buttermilk" marinade by combining all the ingredients in a container large enough to place the tempeh in. Mix with a spoon it will thicken up and slightly curdle.
Once tempeh is done steaming and cool enough to handle place in the marinade. Coating both sides. Cover and place in the refrigerator for at least 40 minutes or up to 3 to 4 hours.
Prepare the slaw by combing the ingredients in a small bowl and refrigerate until ready to use.
Prepare the vegan gochujang mayo be combing the ingredients in a small bowl and refrigerate until ready to use.
Prepare breading by combining ingredients on a flat plate. Mix together to distribute spices evenly.
Once tempeh is done marinating. Evenly coat the tempeh blocks in the breading making sure to cover it as best you can. If you find the breading has turned too wet add an additional tablespoon of flour. If desired spray the tempeh with a cooking spray.
Place the breaded tempeh blocks in the air fryer. Air fry for 17 minutes at 400°F (204°C) or until golden and crispy.
Prepare the gochujang glaze by combining the ingredients in a bowl and mix until well incorporated.
Once the tempeh is done allow it to cool for a few minutes before handling. Then brush the glaze over the tempeh blocks to coat in the sauce.
Assemble the sandwich by spreading the gochujang mayo over the buns. Add a bit of the slaw on the bottom, then place a tempeh block and a bit more slaw.