"Quick, easy vegetarian dinner that is a guaranteed success! This recipe hinges on the quality of the seitan that is used. We make our own. For people in the Northeast, Susie's® sliced seitan is very good and comes in a variety of flavors. We add and subtract veggies based on what finicky kids will eat that day."
Heat 1 tablespoon oil in a skillet over medium heat; cook and stir onion, green bell pepper, and red bell pepper until onion is translucent, 5 to 10 minutes. Add mushrooms; cook and stir until tender, 5 to 10 minutes. Transfer vegetable mixture to a bowl.
Pour remaining olive oil into the skillet over medium heat; add seitan and cook, turning frequently, until browned on all sides, 5 to 10 minutes. Return vegetable mixture to skillet and mix with seitan; season with salt and pepper.
Arrange hoagie rolls on a baking sheet and fill with seitan-veggie mixture. Place 1 provolone cheese slice over the filling of each sandwich.
Heat sandwiches in the preheated oven until cheese is melted, about 5 minutes.