1. Wash and de-vein prawns and marinate in salt and lemon juice for 2 hours.
2. Wash, boil and grind spinach to a fine paste along with curry leaves, green chilli and coriander, using very little water.
3. Mix in crushed black pepper and mustard oil.
4. Marinate prawns in this mixture for another hour.
5. Skewer prawns and grill for 7-8 minutes, basting occasionally.
6. Sprinkle chaat masala and lemon juice over and serve immediately.