Heat oil in a non-stick pan. Add cumin seeds, mustard seeds and black peppercorns and let the seeds splutter.Add asafoetida, mix and sauté for 1 minute. Add green chillies, mix and sauté for 1 minute. Add moong dal and mix well. Sauté for 1 minute.
Add turmeric powder, red chilli powder, amchur and salt. Mix well and cook for 2 minutes.Add ½ cup buttermilk, stir to mix, cover and cook for 3-4 minutes or till dry, stirring once a while.Add remaining buttermilk, stir to mix, cover and cook for 3-4 minutes. Add chopped spring onion greens, mix well for 1 minute and switch off heat. Serve hot.