For the sauce: In a small bowl add the Hoisin sauce, rice vinegar and toasted sesame oil and mix well to incorporate. Set aside.
For the tempeh filling: Heat ¼ cup vegetable broth in a large saucepan. When hot, add the cubed tempeh, ginger, garlic and sauté for a bit then add carrots, water chestnuts, scallions and cabbage. Stir well and sauté for a few minutes, adding additional broth as needed to keep it from burning or drying out. Put the lid on to steam and soften the veggies.
Add the sauce and stir to coat.
Remove from the heat and allow it to cool for a few minutes.
To assemble the lettuce cups, take 1-2 pieces of whole lettuce and place a scoop of the tempeh mixture inside. Garnish with peanuts and cilantro leaves. Serve warm or at room temperature.