Make the seitan In a large bowl combine flour and vegetable stock Stir to make a soft dough Knead for 3 minutes and let rest for 5 minutes
Place seitan in a shallow baking dish Cover with soy sauce and marinate for 30 minutes at room temperature
Preheat oven to 375 degrees Fahrenheit In a large skillet over medium heat heat olive oil Add onion cover and cook stirring a few times until softened about 5 minutes
Add mushrooms vegan sausage parsley thyme salt and pepper Stir for 5 minutes longer then transfer to a large bowl Stir in the bread and mix well Add a small amount of water if the stuffing mixture is too dry Set aside
Place the uncooked seitan reserve the marinade between two sheets of plastic wrap and roll out with a rolling pin until it is approximately 1/4 inch thick Using your hands spread the stuffing over seitan to within 1/2 inch of the edges then roll it up In a lightly oiled shallow baking pan place rolled seitan seam-side down Pierce in several places with a fork
Pour the reserved marinade over the roast and bake uncovered for 40 to 45 minutes basting once after 20 minutes When the surface of the roast is firm and golden brown remove from oven and let rest for 10 minutes
Using a serrated knife cut the roast into 1/2-inch-thick slices Arrange on serving platter and serve with remaining marinade and your favorite vegan gravy
