Place the vital wheat gluten in a large bowl and set aside.
Crumble the tofu into a blender. Add water, oil, nutritional yeast, onion and garlic powder, and poultry seasoning, and process until perfectly smooth.
Scoop the mixture into the vital wheat gluten. Combine with a spatula until a ball of dough begins to form.
Transfer the dough to a work surface and knead vigorously for 4-5 minutes. This is crucial to develop the gluten (see notes above). You can test the dough by stretching it. If it tears easily, more kneading is required.
Cut the dough into 4 pieces and shape each of them into a small oval "chicken breast" fillet.
Lay a sheet of greaseproof paper on a clean surface and place a roughly crumpled piece of yuba, slightly larger than the fillet, in the centre. Place the fillet on top of the yuba, smooth side down so it's in contact with the yuba. Fold the sides of the greaseproof paper over and wrap tightly. Repeat with all the remaining seitan.
Place the tightly wrapped seitan chicken "breasts" into a steamer. A bamboo or an electric steamer will work fine. Steam for 1 hour.
Once steamed, remove the seitan chicken breasts from the steamer and without unwrapping, leave to cool for at least 20 minutes. While the seitan chicken cools, preheat the oven to 400°F (200°C) and make the marinade.