Place a small colander or steamer basket over a small pot of boiling water. Slice tempeh into 4 pieces and place in steamer basket. Steam for about 10 minutes.
While the tempeh is steaming, whisk together the tamari, ginger, agave, garlic, sesame oil, and rice vinegar in a bowl.
Slice the tempeh into bite size chunks and add to the marinade. Let it marinate for as long as you can (at least 10 minutes).
Heat the grapeseed oil in a large skillet or wok over medium heat and add the tempeh. Cook, tossing around a bit so they don't stick, until golden brown.
While tempeh is cooking, whisk the cornstarch into the remaining marinade and add it to the pan, along with the peppers, red pepper flakes, and peanuts. Stir gently (tempeh will crumble if you don't) and serve over rice. Garnish with scallions.