Start by cleaning the Portobello mushrooms with a damp cloth. Remove the stems and gills, then slice them into 1/2-inch thick pieces. Slice the onion and red bell pepper as well, ensuring all your ingredients are ready to go.
In a large skillet, heat 1 tablespoon of canola oil and 1 tablespoon of butter over medium heat. Allow the butter to melt completely and start to bubble.
Add the sliced onions and red bell peppers to the skillet. Sauté for about 5 minutes, stirring occasionally until they become tender and slightly caramelized.
Add the sliced Portobello mushrooms to the skillet, mixing them with the onions and peppers. Pour in the soy sauce and Worcestershire sauce. Sprinkle the dried thyme, and season with salt and pepper to taste. Cook for an additional 7-10 minutes, or until the mushrooms are tender and have absorbed the flavors.
Once the mushrooms are cooked, reduce the heat to low. Lay slices of provolone cheese over the mushroom mixture, covering the skillet. Allow the cheese to melt for about 2-3 minutes.
While the cheese melts, slice the sub rolls and toast them in a separate skillet or under the broiler until golden brown.
Once the cheese is melted and the rolls are toasted, it’s time to assemble your Portobello Cheesesteaks. Spoon the mushroom and cheese mixture generously into each roll, and serve hot!