Toast the bread slices either in the toaster or on a baking sheet placed under the broiler. Let cool.
Preheat the oven to 375 degrees F. Generously butter a 9 by 5-inch loaf pan, then line the bottom with waxed paper and butter the paper.
Tear up the toasted bread slices and make crumbs out of them in a food processor. Place in a large bowl.
Process the walnuts until finely ground and mix into the bread crumbs. Combine the eggs and onions in the processor and process until fine but not liquefied. Stir into the bread crumbs. Place the green pepper, celery, parsley, tomatoes, and oil in the processor and grind until fine but still with some texture. Stir into the loaf mixture along with the poultry seasoning, salt, and pepper. Mix this all very well until evenly moistened. (The mixture may be prepared to this point and refrigerated up to 8 hours in advance.) Scrape it into the prepared loaf pan and smooth over the top. Cover the loaf with foil.
Bake 1 hour and 20 minutes, or until a knife inserted in the center of the loaf comes out dry. Let sit 5 minutes, then run a knife all along the sides of the loaf to help loosen it. Unmold the loaf onto a platter and remove the waxed paper. Let the loaf cool 20 minutes or so before slicing it. It's best to serve the loaf warm and the gravy hot.
Melt the butter in a medium-size saucepan over medium heat. Add the mushrooms and saute until brown, about 7 minutes. Stir in the flour; it will become very pasty. Cook this roux for 2 minutes, stirring constantly. It will stick to the bottom of the pan a little bit; that's okay.
Stir in the stock, wine, soy sauce, and pepper, and bring to a boil. Cook the sauce at a lively simmer for 5 minutes, stirring almost constantly and scraping any crusty bits that adhere to the bottom of the pan. Serve in a sauceboat.
Recipe courtesy of Jeanne Lemlin, Vegetarian Classics, HarperCollins, 2001