Soy mince is easy to find in any supermarket now, but here is a homemade soy-free mince for allergy sufferers or those looking for an alternative option.
Put the walnuts in a food processor and pulse until chopped. Add the rest of the ingredients and pulse until you have a chunky mixture. If you don’t have a food processor, finely chop the mushrooms and bash the walnuts, wrapped in a clean towel, with a rolling pin, until crushed, then mix with the rest of the ingredients.