1. Prepare the seitan using any recipe from this website. Reserve the liquid you use to boil it in; you can use it later to make the gravy.Add mushrooms to a small food processor or spice grinder, and grind them into a fine powder. I like to use this powder for seasoning soups and whatnot, but its especially good for this mushroom gravy.
2. To make the gravy, add 1 tablespoon vegan margarine and 1 tablespoon whole wheat flour to a frying pan. Cook until slightly frothy and the flour darkens a little (about 1-2 minutes of well-supervised stirring). Add about 3/4 cup broth and a splash Braggs (or boiling liquid from seitan) to the pan, and stir until smooth.
3. Add a few tablespoons of the dried mushroom powder and stir until smooth. Bring up to a boil, then cut off the heat and add nutritional yeast. If the gravy is too thick, add a little more broth. If its too thin, add a little more mushroom powder and/or nutritional yeast. If its bland, add a little more Braggs, and season with salt and pepper.
4. Place squash cut-side down in a shallow dish of water and microwave for about 10 minutes. Use a fork to scrape out the spaghetti and season with a bit of salt and pepper.
5. To serve, assemble shallow bowls with spaghetti and small seitan cutlets, topped with lots of mushroom gravy. Add peas and/or greens, if desired.