Soak walnuts in a bowl of boiling water for at least 30 minutes.
Preheat oven to 200 °C(390 °F) and prepare a baking tray by placing a sheet of parchment paper on to.
Place onions and mushrooms in food processor and pulse until chopped evenly.
Heat olive oil in large pan over medium-low heat and add in mushrooms and onions. Season with salt and pepper and cook, stirring occasionally for 10-15 minutes until onions are golden brown and mushrooms have softened. As soon as the mushrooms have expressed their moisture, turn up to high heat to try to cook off the moisture.
Meanwhile, drain and pulse the kidney beans in the food processor. You don't want it to be mushy but just chopped/ combined slightly.
Then, once the walnuts are done soaking, drain and pulse in the food processor until small pieces remain. Add into the mushroom mix along with the beans, garlic, red wine, soy sauce, balsamic vinegar, miso paste and mustard and mix to combine. Continue cooking for another 10-15 minutes until flavours are melded together and most of the moisture has evaporated.
Unroll the puff pastry sheet onto the prepared pan. Spread the mushroom mixture in the centre, ensuring to leave an extra 2cm border at the edge of the pastry.
Very carefully roll the pastry over the top of the mushroom mixture until you have a log. Pres down to seal the edges and roll the log so the seam is facing down.
Score the puff pastry if desired with a knife in the desired pattern.
Brush with non-dairy milk and place the pastry in the freezer for ten minutes prior to placing in the oven.
Place the pastry in the oven for 30-35 minutes or until golden and flakey.
Serve with all the roast fix ins and vegan gravy.