With ¼ of the seitan recipe, slice the seitan thin.

Combine the marinade ingredients and add the thinly sliced seitan.

Marinate for 1-2 days in a refrigerated covered in a refrigerator-safe container.

Preheat an oven to 350 degrees.

Place a single layer of vegan roast beef on the pan covered with a silicone baking mat or parchment paper on a baking sheet.

Pour the remaining marinade over the vegan roast beef pieces.

Bake uncovered for 30 minutes.

Mix the vegan cashew mayo with the pure horseradish.

Cover and refrigerate until ready to serve.

In a saucepan, saute the shallot and onion until translucent.

Add a little of the vegetable broth if the shallots and onions begin to stick.

Then add the rest of the ingredients, bring to a boil, and then reduce heat to simmer.

In a large non-stick skillet, combine the minced garlic and sliced onions.

Saute on medium-low until the onions turn translucent.

Add the mushrooms and cook until the onions appear to brown, and then add a little vegetable broth and move the onions and mushrooms around the pan with a skillet.

Add more vegetable broth as the onions and mushrooms brown and caramelize.

Set aside.

Toast the ciabatta buns.

Add pieces of vegan roast beef to the bottom bun.

Now, add sauteed mushrooms and onions.

Smother with vegan horsey sauce or your favorite condiment.

Top with the other toasted bun.

Cut each sandwich in half.

Serve with a bowl of hot au jus dipping sauce.