Break bread into 1 inch / 2.5 cm thick chunks; dry in a large bowl, uncovered, at least 8 hours.
Melt margarine in a large nonstick skillet over medium-high head. Add carrot, celery and onion; saute, stirring frequently, until lightly browned. Transfer to a large mixing bowl; cool to lukewarm. Add pepper, bread cubes, parsley, sage, egg substitute or Egg Replacer, and broth or water. Toss to combine; set aside at least 30 minutes to allow liquids to soak into bread.
cook oil garlic and onion until the onion is tender and clear. Add in the flour, yeast and soy sauce (it will make a paste), slowly add in the broth as you bring the mixture to a boil. Then add the salt (if needed) and pepper.
Preheat oven to 400F/205C. Line a baking sheet with heavy-duty foil; spray foil with nonstick cooking spray.
Brush seitan with gravy on both sides, arrange overlapping slices on foil in a row, mounding in center. Press stuffing mixture around seitan to cover completely. Wet hands lightly, and press into a neat oval.
Roll pastry sheets out to 1/16 inch / 2 mm thickness; arrange, overlapping slightly, to make a large rectangle. Seal edges with dabs of cold water.
Drape pastry over mound; trim excess away around bottom. Use scraps to cut out decorative shapes (leaves, apples, etc.); attach with dabs of cold water. For a shiny crust, brush pastry lightly with soymilk. Bake 1 to 1-1/4 hours, covering pastry with foil if it browns too much.
Transfer 'turkey' to a platter. To serve, cut straight down through pastry, stuffing and seitan to make neat 3/4-inch slices. Spoon gravy over each serving.
posted by mincus