Heat the oil in a large pot over medium heat. Stir in the onion and garlic, and cook 5 minutes until onion is tender. Mix in quinoa, lentils and mushrooms. Pour in the stock. Cover, and simmer 20 minutes.
Remove the pot from heat. Chop chard, and gently mix into the pot. Cover, and allow to sit 5 minutes or until the chard is wilted.