Prepare the teriyaki sauce: In a bowl, mix the soy sauce, mirin, brown sugar, rice vinegar, ginger and garlic. Set aside.
Cut the seitan: Cut the seitan into thin slices.
Cook the vegetables: In a large skillet, heat the sesame oil. Add the sliced onion, the julienned carrot, the sliced courgette and the striped pepper. Cook for 5-7 minutes.
Add the seitan: Combine the seitan with the vegetables and cook for another 5 minutes, until golden brown.
Stir in the sauce: Pour the teriyaki sauce onto the pan and cook for 2-3 minutes, stirring well, until the sauce thickens.
Serve: Transfer everything to a serving dish, garnish with sesame seeds and serve hot.
Enjoy your meal!
