Grind Ginger, Garlic & Coriander leaves. Grind Coconut and keep it separately.
Pour Oil in a Vessel fry the sliced Onions, Curry Leaves & Green Chillies , when the Onions are getting brown add the ground Masala, Salt, Turmeric Powder & fry nicely till the oil comes to the surface, now add the chopped Tomatoes & continue to fry the Masala till the Tomatoes are soft, add the ground Coconut paste, mix well, add the Crabs, required quantity of water & cook till Crabs are done & flavour escapes. Remove from Fire & Garnish with the Chopped Coriander leaves.