Cut the mushrooms lengthwise and wash in water with little turmeric powder. Slice onions, chop ginger, garlic, tomatoes and coriander leaves. Heat oil, saute onions, add ginger, garlic, tomato and green chillies and saute well. Add mushrooms, half cup water and salt to taste. Cook till mushrooms are tender and gravy is thick. Serve hot, garnished with coriander leaves and fresh cream.