This lovely soup is simple to make and tastes terrific. Traditionally osaman is made with toor dal (split pigeon peas), but in my house it is made with sabut moong, which is equally good.
Put the sabut moong in a bowl, wash in plenty of water 2 or 3 times, and drain. Add 2cups (400ml) water and soak for about 30 minutes. Drain in a colander.