Step 1

If using homemade seitan pepperoni, slice it thinly, place in a bowl and drizzle with olive oil. Toss to coat, and set aside.

Step 2

Preheat the oven to 375 degrees F, and lightly oil a 13x9 casserole dish.

Step 3

Bring a large pot of salted water to a boil, and cook pasta for 2 minutes less than indicated on the package. Drain in a colander. While the pasta is cooking, move on to step 4.

Step 4

Preheat a saute pan over medium heat. Cook the onion, mushrooms, and bell pepper for 5 to 7 minutes or until the moisture from the mushrooms has evaporated. Add the oregano, garlic powder, pepper flakes, and a generous pinch of salt and pepper. Cook for another minute and remove from heat.

Step 5

Return the pasta to the pot and combine with marinara, sauteed veggies, olives, and a pinch of salt and pepper. Fold in the pepperoni slices, reserving a handful to decorate the top of the dish if desired. Cook the pasta mixture over medium heat just until hot, about 2 minutes.

Step 6

Spoon half of the pasta mixture into the prepared dish. Add a generous layer of shredded cheese, about 1 cup, followed by the rest of the pasta. Drizzle the boiling water into the dish (this helps the cheese melt).

Step 7

Top with reserved pepperoni and remaining cheese, and cover the dish tightly with foil. Bake for 25 to 30 minutes or until the cheese is melted. Serve hot.