Place the tofu, butter beans, bean water from the tin, mushroom bouillon, olive oil, sea salt, miso paste and rice vinegar into the largest cup or jug attachment of a high speed blender.
Blend on high speed for a minimum of 1 minute. Remove the cup, shake it well or use a spatula to make sure no chunks are stuck to the side then blend again for another 30 seconds until very smooth and creamy.
Add the vital wheat gluten to the mixture and blend on low speed until the mixture comes together. Increase the speed to medium for at least 1 minute. At this stage, the seitan dough should be very smooth and stringy – almost like the texture of tough chewing gum (don't worry – this is correct – it won't be like this once cooked!). Remove the dough and wrap in reusable wrap or a plastic bag, to stop it from drying out.
Place the yuba into a deep baking tray and cover with boiled water. Leave to hydrate for a few minutes then discard the water. Set the hydrated yuba aside.
Divide the seitan chicken dough into 8 pieces, roughly 150g each. Working with one at a time, pinch the edges of the piece of seitan and tuck it over and into the centre, making one smooth side and one folded, tucked side. Roughly shape the dough into a fillet. Repeat with the remaining pieces.
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.
IMPORTANT: it's essential that each fillet is wrapped as tightly as possible otherwise the seitan will expand and become spongy rather than firm and meaty. If you have heat-safe cling film, use this to wrap around the greaseproof paper tightly and secure it in a roughly fillet-like shape. Alternatively you can use muslin or cheesecloth bound with thread. Aluminium foil will also work.
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 200c (fan) and make the marinade.
'Chicken' will need to be roasted with the veg (see below)