Heat coconut oil in the pan on medium heat.
When the oil is hot enough add finely chopped onions and saute them until golden brown. Add little salt, just enough for the onions and ¼ tsp turmeric as soon as you add onions. Salt brings the water out of onions and help them cook faster.
When the onions turn golden brown add 2 tsp ginger garlic paste, 2 tsp coriander powder, 1 tsp cumin powder, and 1 tsp red chilli powder to the onions and mix well. Let the spice powders cook well without burning them.
Now on medium high add chopped tomato pieces or tomato puree, little more salt for tomatoes and mix well. Let the tomatoes cook covered until they are soft and mushy and oil separating to the sides of the pan. Keep stirring in between to avoid burning.Add little water if necessary. Add 1 tsp of sugar if the tomatoes are too sour to balance the flavours.
Now reduce the heat to medium and add the can of full cream coconut milk, crushed kasoori methi leaves (crush them between your palms to make fine powder) and mix well. Let it cook for 4 to 5 mins, and add more salt and chili powder if needed. Sauce should be completely cooked and seasoned as you want before adding salmon.
Now add the Salmon fillets carefully into the gravy on medium low heat, making sure they are not on top of each other, thus giving them enough space to cook. Cover them with sauce on top.
After 5 to 8 mins, check with a sharp knife or fork at the thickest part of the fillet. If it is flaky and turned to opaque pink, it is done. If u want you can check for the minimum internal temperature of 145°F(USDA recommendation), which should be measured at the thickest part of the fillet.
Now add chopped cilantro to garnish and serve hot with Rice.