Cut the seitan into 1-inch cubes and place in a bowl.
Combine soy sauce, ponzu sauce, and 1 1/2 teaspoon cornstarch in a small bowl. Mix until cornstarch dissolves and pour over seitan. Set aside to marinate for 10 minutes.
In a separate bowl, combine mushroom broth, soy sauce, hoisin sauce, sesame oil, 1 teaspoon cornstarch, and Sichuan pepper. Mix until cornstarch dissolves. Set aside.
Heat the oil in a large wok over medium-high heat. Add chilies, stir-fry for about 30 seconds. Add marinated seitan and mushroom broth sauce and stir for 2 to 3 minutes. Add scallions, garlic, ginger, and sesame seeds. Stir-fry for a few more minutes. Remove from heat.
Serve over brown rice, garnished with salted peanuts and extra scallions.
Note: Ponzu Sauce often has fish in it. If you can’t find a vegan version, an acceptable substitute would be 1 teaspoon orange juice, ½ teaspoon mirin and ½ teaspoon rice vinegar.