Place tempeh in a steamer basket and set over a pot with 1” of water. Bring the water to simmer, cover and let steam for 10 minutes. This step helps the tempeh to become tender and ready to soak up the flavors of the marinade.
In a small bowl, whisk all remaining ingredients until well combined to create a marinade.
Place steamed tempeh in a shallow dish and pour the marinade over the top to coat. Marinate for at least 30 minutes, up to overnight.
Preheat oven to 425°F and line a baking sheet with parchment paper.
Arrange the cubes on the prepared baking sheet, reserving excess marinade.
Bake 10 minutes. Remove from the oven and brush more of the marinade onto the cubes. Bake an additional 10-15 minutes, or until the cubes are charred around the edges.