Put potatoes in pan with just enough water to cover. Bring to a boil, then simmer until soft. When you drain the potatoes, save the starchy potato water for use in the mushroom gravy. Mash them until they're the consistency you want.

Sauté the chopped onion in oil with thyme, coriander, and black pepper until onions are translucent. Add chopped walnuts and shredded tofu. When heated through, stir in lemon juice and tamari. Remove from heat.

Sauté mushrooms, tamari, and black pepper in oil. The recipe says to sauté until tender, but if you fry the mushrooms until they express most of their liquid I find it helps keep the Shepherd's Pie from getting watery in the oven.

Dissolve the arrowroot in the hot potato water and slowly add the mixture into the sautéed mushrooms, bringing it to a low boil. Continue to stir until the gravy is thick and clear.

Place the tofu mixture in a casserole dish first, then the mushroom gravy, and layer the potatoes on top. Bake at 400° for 15-20 minutes, or until top starts to brown.