Heat the oil in a skillet over medium-high heat.
Add the onion and mushrooms and cook for 5 minutes, or until the liquid from the mushrooms has evaporated.
Stir in the brown rice, walnuts, and cumin.
Cook for 30 seconds to toast the grains and coat them with oil.
Pour in the water or vegetable stock and salt.
Bring the mixture to a boil.
Cover the skillet, reduce the heat to low, and simmer for 45 minutes, or until the liquid is absorbed and the rice is tender.
Fluff with a fork and serve garnished with fresh parsley.