Cut the tempeh into slices, between 0.25 - 0.5 inch thick.
Steam or poach the tempeh for 2-3 minutes. (to poach, simmer the tempeh in just enough water to cover.)
Remove the tempeh from the hot water and set aside.
In a mixing bowl, whisk together all the marinade ingredients until they are well mixed
Add the tempeh slices to the marinade, stir gently to coat.
Allow the tempeh to marinate for at least 30 minutes. You can also keep the marinating tempeh in the fridge for up to 2 days. The longer you marinate the tempeh, the more flavour it will absorb.
Cook the tempeh on a hot grill, basting a couple times. Turn once to grill on both sides. Be sure to reserve a few tablespoons of the marinade!
When the tempeh is golden brown on each side, remove from heat.
Drizzle the last of the marinade over the tempeh and sprinkle sesame seeds on top (if using). Serve immediately.