Deshell and devein the prawns; clean well, wash and drain.
Blend the cashewnuts, ginger, garlic, green chilli, turmeric powder, chilli powder, garam masala and kasuri methi to prepare the marinade.
Place the prawns in a glass bowl, season with salt and add the marinade. Mix well to coat the prawns evenly and keep aside for atleast 1 hour (longer, if possible).
Heat enough vegetable oil in a pan to shallow fry the prawns.
Once the oil is hot enough, pan fry the prawns in batches till done.
Sprinkle chaat masala on the fried prawns and serve warm with lemon wedges.