- Preheat oven to 180°C (350°F).
- In a saucepan, melt 60 mL (¼ cup) of margarine over low heat. Add flour and cook for 1 minute while stirring. Slowly whisk in vegetable broth until no longer lumpy.
- In a bowl, dissolve miso in hot water. Add miso liquid, soy sauce, onion powder, and pepper to broth and bring to a boil. Reduce heat to medium and whisk until sauce thickens. Set aside.
- Melt 5 mL (1 tsp.) of margarine in a skillet set over medium heat. Add mushrooms and cook until golden, about 5 to 7 minutes. Stir in reserved sauce.
- Cut baguette into two 15-cm (6-in) long pieces and cut in half to open.
- Thinly slice seitan loaf. In a skillet set over medium heat, add coconut oil and brown both sides of each seitan slice.
- Place roasted seitan slices in each baguette and top with grated cheese. Keeping sandwich open, place on a baking sheet and bake for about 10 to 15 minutes, or until cheese melts. Remove from oven and pour sauce over sandwiches. Enjoy!