Put chopped fresh coriander,mint leaves,curd,garlic,Green chillies,garam masala,salt to a blender. Blend till smooth. Don't add any extra water.
In a pan on medium heat roast gram flour till fragrant and light golden in colour.
In a container with lid put the prawns,the green paste,gram flour,assorted pepper,Onion and tomatoes. Mix well,refrigerate to marinate at least for 2 hours.
20 minutes before grilling take the marinated prawns out of the refrigerator.
Heat a iron griddle pan. Spread 1 tbsp oil/butter. Once it is really hot, pick only the prawns from marinade.Arrange them on the hot pan. let it grill for 2-3 minutes each side. (I would suggest to grill prawns in batches for even cooking). the prawns should be cooked done with beautiful charred effect. Note : It is better to grill prawn and veggies separately,to avoid over cooking of prawn. Over cooking results in rubber like prawns.
At the end transfer all the veggies along with the leftover marinade. Grill till they are half done(I like them a bit crunchy) and look charred.
Sprinkle generous amount of chat masala and serve hot.