Fill a saucepan with an inch of water and bring to a boil. Add tempeh and reduce heat to simmer. Simmer for 10 minutes to remove any bitterness and soften the tempeh.
Remove tempeh from water and cut into desired shape.
Mix together remaining ingredients. Add extra water as needed to thin the sauce for marinating.
Place tempeh in a container or zip lock bag and pour marinade over. Mix the tempeh around so all sides get coated in sauce. Marinate for at least 30 minutes, the longer the better.
AIR FRYER: Air-fry at 350°F for 10-12 minutes until golden brown and crispy.
OVEN: Bake on a parchment paper-lined baking sheet at 375°F for 20-30 minutes until golden brown and crisp. Flip the tempeh after about 15 minutes.