Take the marinated seitan.
Heat half of the oil in a wok and add the seitan. Toss well to cook.
Once the seitan pieces are browned, take out from the wok and set aside.
Now add rest of the oil to the wok.
Add the dry chilies and cook until they are fragrant and brown.
Now add, ginger and garlic and saute for a few seconds.
Now add celery, red bell pepper and zucchini. Toss well.
Stir fry for few minutes until vegetables are half cooked.
Now add the kung pao sauce mixture and ¼ cup of water or vegetable broth.
Bring the mixture to a boil. As the sauce starts to bubble, add the seitan and mix well.
At this point, mix well to avoid the sauce sticking to the wok.
Add pistachio nuts and chopped scallions.