Put 12 cups of water on to boil in a large (at least 6-quart) soup pot. Add each vegetable (potatoes, onion, celery, mushrooms, carrots) to the pot as you chop it. Add the bay leaves, thyme, sage, garlic, poultry seasoning, onion powder, celery salt, soy sauce, pepper, and salt. Bring to a boil and reduce heat to simmer uncovered for about 20 minutes.
Meanwhile, prepare the seitan: Mix the dry ingredients in a medium-sized bowl. Combine the broth and nut butter. Stir the broth mixture into the dry ingredients until well blended. Knead gently 10 times. Turn out onto a cutting board and press it as flat as possible. Let it rest for about 5 minutes. Then using a sharp knife, cut it into 1/2-inch cubes. Add the seitan cubes to the simmering vegetables, taking care to separate them before they go into the pot. Stir well and simmer for 45 minutes, stirring occasionally.
After 45 minutes, remove the bay leaves and add the peas. Mix the miso in a small bowl with a little of the hot broth, and then add it to the stew, along with the nutritional yeast. Stir in the cornstarch mixture and bring to a boil, stirring often. When mixture thickens, reduce heat and allow to simmer while you make the biscuits. (If stew does not seem thick enough, add a little more cornstarch/water.)
(You can make the recipe up until this point the day before serving and refrigerate the filling. When ready to assemble, reheat the stew as you make the biscuit topping. Stew should be hot when the biscuits are placed on top.)
Preheat oven to 400 and oil two or more deep casserole dishes (any combination of casserole dishes or pie pans to hold about 6 liters). Mix the dry ingredients for the biscuits in a medium bowl. Stir in the pumpkin and the soymilk/lemon juice. Add additional soymilk or water a teaspoon at a time as you stir until all flour is moistened and dough forms a ball. Turn out onto floured board and knead two or three times. Roll out to 1/2- inch thick, and cut into circles using a 1 1/2-inch wide floured glass or biscuit cutter. Gather remaining dough and use it to cut additional biscuits. You should have between 24 and 30. (Alternately, cut the biscuit dough to fit the pans, leaving about an inch all around to allow for dough to expand.)
Pour the stew into the prepared pans, making sure there is at least 1/2-inch free at the top. Place the biscuits on top, spacing them evenly. Bake until biscuits are lightly browned, 15-20 minutes. Remove from oven and allow to stand for a few minutes before serving.
Decrease sodium by eliminating the salt.