In a saucepan, saute onion in oil for 1 minute. Stir in the mushrooms, carrot, garlic and ginger. Cook and stir until vegetables are almost tender. Stir in the broth, soy sauce and lemon juice. Bring to a boil. Stir in couscous. Remove from the heat; cover and let stand for 5 minutes. Fluff with a fork.