Step 1

In a large mixing bowl, mix all of the ingredients together until fully combined.

Step 2

Slice 1 pound of seitan thinly. Place it in a large, shallow baking dish. Pour the marinade over the seitan and marinate in the refrigerator for 1 to 2 days.

Step 3

In a small mixing bowl, whisk together all of the ingredients. Set aside.

Step 4

In a large skillet over medium-high heat, warm the oil. Add the onion and peppers and sauté for 7 to 9 minutes, until the onion is translucent. Remove from the heat and transfer the onion and peppers to a medium covered bowl. Set aside.

Step 5

Place the sauerkraut in the skillet and return it to the heat. Warm it in the skillet for 5 minutes, until it is warmed through. Remove from the heat and transfer the sauerkraut to a medium bowl. Cover the bowl and set aside.

Step 6

Toast the bread. Place the Seitan Corned "Beef" in the skillet and return it to the heat. Warm it in the skillet for 5 to 7 minutes, until it is warmed through and a little brown on the edges. Remove from the heat and set aside.

Step 7

Place 4 of the toasted bread slices on a serving platter. Divide the Seitan Corned "Beef" evenly among the 4 slices.

Step 8

Atop each pile of Seitan Corned "Beef," layer 1/4 of the sauerkraut, the pepper-onion mix, the vegan mozzarella cheese, and the Thousand Island Sauce. Top each sandwich half with the remaining 4 slices of bread. Slice each sandwich in half and serve immediately.