There are two separate parts and they can be cooked at the same time.
Chop mushrooms, spinach and garlic.
Green chilly and red chilies for some heat.
Heat butter. Saute garlic and chilies.
Add mushrooms and cook till they turn slightly brown.
Add some onion powder and mix it well.
Add the chopped spinach and now cook it covered for 5-6 mins on low heat.
Open and you will find a lot of water in the dish. Cook on high heat till the water fully evaporates.
Heat oil and add red chilly powder, turmeric powder and coriander powder.
Lightly heat it and then add the fish to it, skin side down.
Using a spoon coat the top as well.
Cook till the color changes beyond the halfway mark of the fish.
Flip it over.
If you are very particular use a thermometer to check the thickest part. If its 65 degrees Celsius the fish is fully cooked.
Remove on a tissue paper to drain the extra oil.
You don’t need to heat the dish at time of eating it.
Will be fine even at room temperature.
There is no salt in the fish. If you want, season it at the time of eating it.