Heat the oil in a medium saucepan and sauté the onion and garlic for 5 minutes, until softened. Add the balsamic vinegar, yeast extract or miso paste and mushrooms and cook for a further 8 minutes until brown and sticky. Remove from the heat and allow to cool for 10 minutes.
Add the mushroom mixture to a food processor along with the beans, walnuts, oats, flour