Make cuts on the tomatoes and boil them until smooth. Remove the skin and make a smooth paste.
Add warm water to the tamarind, soak for a while and extract thick pulp.
Add half of the oil to a deep bottomed pan, heat and fry the marinated crab pieces. Remove and save.
Add remaining oil to the pan and add onion pieces. Fry till brown. Add onion paste, tomato paste, green chilly pieces and fry till oil shows up. Now add the coconut paste and fry till the entire contents turn brown.
Add the fried crab pieces, garam masala powder and enough salt. Mix well, fry for a couple of minutes and add the tamarind paste and some water. Mix thoroughly and allow to simmer on medium flame till the preparation is well done.
Remove the pan from the stove, top the preparation with chopped coriander leaves.