Rub the fish with 1 teaspoon of turmeric powder & ½ teaspoon salt and set near while you prep the vegetables.
Add garlic and roughly chopped green chili to a mortar pestle and pound coarsely.
In a heavy bottomed pan, add the oil and heat up till you see ripples on the surface. If using mustard oil, you will need to heat it till its slightly smoking to do away the raw smell.
Reduce heat to medium and add fenugreek seeds, ginger and garlic green chili paste to oil. Take care not to burn. Take the pot off the stove if needed. Saute for 15 seconds or so.
Next, add the onion and cook them till golden brown. About 5-7 minutes.
Add 2-3 tablespoon water and add the coriander cumin, kashmiri chili and turmeric powder. Saute the spices for a minute or so in oil.
Next, add the tomatoes and salt. Cook this masalaÂ on low heat till the oil starts separating from the mix along the sides of the pan. About 8-10 minutes.Cook thoroughly to reduce moisture of tomatoes. This will help develop flavors and color of the curry, please do not rush. Allow to reduce till masala acquires beautiful reddish to brown color.
Carefully, layer the fish in a single layer over the onion tomato masala. Sprinkle ½ teaspoon salt. Stir around gently using a wooden spoon so that the fish is coated in the masala. Let cook for a minute and using a wooden spoon flip. Add warm water and then cover the pot. Cook for 8-12 minutes or until the fish is cooked through.
Finish with kasuri methi, amchoor (or lemon juice) and garam masala. Sprinkle some cilantro before serving.