Take fish and the marinating spices and mix well. Set aside.
Soak tamarind in some water, squeeze them well and strain it and set aside.
Heat a earthernware pot, add in oil and crakle in mustard, fenugreek, dry chilli and curry leaves.,
Add in onions and green chillies. Add in salt and mix well. Cook till it gets lightly translucent.
Add in tomatoes and cook till it gets mushy, add in the spice powders along with a splash of water and mix well. Cook till oil separates.
Now add in tamarind water and salt, add more water as needed. Bring it to a boil.
Now add in fish and mix well. Bring it to a boil again and simmer for 10 to 15 mins.
Now add in fresh curry leaves and coriander leaves.
Mix well and serve over rice.