Dry-roast chana dal for 10 minutes over moderate heat. Cool. Coarsely blend coconut, green chillies, mint, garlic, ginger, salt and chana dal in a food processor. Heat oil in a frying pan and cook mustard seeds, urad dal, dried chillies and curry leaves until seeds start to pop. Stir into coconut mixture, then add asafoetida. Refrigerate in a sealed jar for up to 2 days only.