To make the marinade, add coriander leaves, mint leaves, vinegar, ginger, garlic and green chilies to a grinder jar and grind together.
Now add water, 1 tablespoon at a time, for easy blending. The mixture should be thick and not too watery. You may or may not need half cup of water.
Transfer the mixture to a bowl and season with salt and pepper to taste. Add the olive/vegetable oil to the marinade and mix well.
Score the pomfret both sides with the edge of the knife. Season both sides of the fish lightly with salt. Apply the coriander-mint marinade over the fish on both sides in thick layer.
Pack each pomfret in aluminum foil making sure there is no gap and no steam is able to escape.
Place the packed fish on the steamer on top of simmering water making sure water is not touching the foil. Cover and steam the fish for 10 minutes, then flip it over and steam for another 10 minutes.
Serve the hot steamed fish with Basmati rice.
Recipe by Flavor Quotient at https://flavorquotient.com/2017/02/patrani-machhi-steamed-fish-in-foil/