Apply salt and lemon juice to the fish pieces and set aside. Hang yogurt in a muslin cloth to remove excess water. Dry roast besan on low heat until it is cooked well. Soak saffron in warm milk. Combine besan and hung yogurt and rub thoroughly until smooth.
Then mix ginger paste, garlic paste, green chillies, garam masala powder, turmeric powder, salt and saffron dissolved in milk.
Mix thoroughly. Refrigerate fish pieces in this marination for about thirty to forty minutes preferably in the refrigerator. String the fish pieces on to skewers and cook in tandoor or grill until done. Serve hot sprinkled with chaat masala.