Cut the tempeh by slicing in half lengthwise then slicing into triangles. If the block of tempeh is thick you may also want to slice it in half widthwise.
Fill the bottom of large skillet with approximately 1-inch of water and bring to a low boil. Reduce to a simmer then carefully place the tempeh triangles into the water. Cover with a lid and allow to steam for 10 minutes.
Meanwhile, prepare the peanut sauce. In a large shallow bowl, whisk together the peanut butter, tamari, rice wine vinegar, garlic powder and crushed red pepper. Add water 1 tablespoons at a time to thin until a smooth sauce forms. For me this was about 4 tablespoons. Taste test to see if you prefer more flavor and add more of each ingredient according to your preference. Reserve 3-4 tablespoons of the sauce for coating prior to serving as the tempeh will dry out a bit after baking.
Once the tempeh is done steaming, transfer them to the shallow bowl and stir until evenly coated. Allow to marinate for at least 30 minutes or up to overnight. If you let it sit for longer than 2-3 hours or if the room temperature is greater than 75°F then you’ll need to cover and store in the refrigerator.
When ready to cook, preheat the oven to 400°F. Line a baking sheet with parchment paper or a silicone mat. Arrange the tempeh on top then bake for 15 minutes, flipping halfway through.
Brush with reserved peanut sauce, serve warm and enjoy!
Depending on the peanut butter you use you may want to add salt or sugar (such as coconut sugar or maple syrup) to the marinade. Make sure to taste test and add flavorings as desired.