In a large bowl, stir together the vital wheat gluten, chickpea flour, onion powder, garlic powder, and salt.
Add the water or vegetable broth and stir into a dough. Turn out onto a work surface and knead for 5-10 minutes. The more you knead, the more meat-y your seitan will be. If you’re looking for seitan that can shred, knead longer. If you want more tender seitan, knead for less time. Cover and let the seitan rest for 5 minutes.
While the seitan is resting, bring the vegetable broth, onion, carrot, celery, and soy sauce up to a boil in a very large pot then turn the heat down to the lowest it will go, so that it’s barely simmering.
Cut the dough into at least 4 large pieces and shape. You can also cut or pull the dough into small strips or chunks.Optional: Shape and wrap the seitan in foil before simmering. This will give you a more dense, meaty texture because the seitan won’t have as much room to expand.
Add the seitan to the barely simmering broth and cook, uncovered for 1 hour, making sure it doesn’t come to a boil.
When the hour is up, remove from the heat and let cool. Use immediately or store in the broth for future use. Refrigerate for up to 1 week or freeze.