Place the tamarind paste in a large bowl and pour 3 cups of hot water over it. Break up the paste using a couple of forks, and allow to sit for 30 minutes. Strain, save the broth and discard the pulp and seeds. Set aside the broth.
In a medium sized frying pan, saute the onions for about 10 minutes or until lightly golden.
Add the minced garlic and saute for an additional 2 minutes.
Add turmeric, stir for another minute until the onions have turned brilliantly golden. Remove from the heat and set aside.
While the onions are cooking, in another large frying pan, heat the oil and saute the chopped cilantro and green onions over medium high heat for 15 minutes.
This is an important step in developing flavors. Initially the herbs are sauted on higher heat to evaporate the moisture, then the flame is lowered and the herbs are constantly stirred to prevent them from sticking to the bottom of the pan. The herbs will develop a darker green color and become quite aromatic.
Once the herbs have been sauteed, add the fenugreek leaves, salt and chili pepper and saute for an additional minute. Add a touch more oil if the herbs look too dry and stick to the pan.
Add the sauteed onions and tamarind broth, bring to a gentle simmer, cover and cook for 30 minutes.
While the herb sauce cooks, sprinkle the salt over the fish and saute the fish over medium heat with the skin side down for about 5 minutes.
Place the fish over the sauce, cover and cook for another 5 minutes. Fish should be firm but not overcooked.
Gently place the sauce and the fish in a serving ware and serve with Persian basmati rice.