Wash the moong dal well and soak it in water for an hour or until it is soft. In a blender, grind the soaked moong dal along with the red chillies, cumin seeds and salt into a fine paste by adding little water. The paste should be thick, so add the water only as required.
Transfer the finely ground pickle into a serving bowl, add the lemon juice and mix well.
In a small pan, heat the oil and add the mustard seeds.
When they splutter, add the cumin seeds, the dals and the curry leaves. Fry them until the dals turn golden brown.
Finally, add the above seasoning to the prepared pickle and mix well.