Rinse the quinoa in plenty of cold water and place in a medium saucepan. Add boiling vegetable stock and bring back to the boil. Simmer over medium-low heat for 15 minutes until the stock is absorbed and the quinoa is tender.
Meanwhile, heat oil in a frying pan and saute onion for 2-3 minutes, add the garlic a fry for another minute. Add sliced mushrooms and season with salt and pepper. Finally, add the thyme leaves. Stir fry the mushrooms for about 5 minutes, or until soft.
In a small bowl, mix the cooked quinoa with olive oil, add mushrooms and tomatoes, mix well. Check the seasoning and add more salt or pepper if you like. Scatter fresh parsley on top and serve.