Heat the oil and fry the onion and garlic until soft, about 8 minutes. In a food processor, process the cashew nuts until finely ground, then mix with the breadcrumbs. Mix in the mashed parsnips and herbs. Add the onion, and be sure to scrape all the juices into the mixture.
Dissolve the yeast in the water and mix into the vegetable nut mixture. Season well with salt and pepper.
Melt the butter in a skillet and saute the chopped mushrooms until soft, about 10 minutes. Grease a 2-pound loaf pan and press in half the nut mixture. Cover with a layer of mushrooms and top with the rest of the nut mixture.
Press down well. Cover with foil and bake for 1 hour. When cooked, remove the pan and let stand for 10 minutes before turning onto a plate. Serve hot or cold. Slice to serve. Serve with vegetables or a crisp green salad. This would be good with gravy too. Enjoy!