Wash and clean the salmon head and remove the gills. Slice into serving pieces if desired. Drain in a colander.
Place in a bowl and rub with salt and pepper. Heat oil in a non-stick pan about 1 Tbsp. and lightly fry the salmon head about half a minute on each sides. Set aside in a bowl.
In the same pan, add another tablespoon of oil and saute garlic, onion and ginger for a few minutes. Add in the tomatoes and saute. Simmer until slightly tender.
Pour in patis and simmer for a minute. Then add in the miso and stir. Add also the sinigang sa sampalok mix and stir again.
Pour 1/2 cup of water and stir until the miso and sinigang mix is dissolved.
Pour 2 liters of rice washing or water in a pot and transfer the sauteed aromatics and miso from the pan to the pot. Bring the rice washing to a boil. Season with salt and pepper.
Add in the mustard leaves and long green chilies. Then put all the salmon head pieces in the pot and simmer for 3 minutes. Then turn off heat. Serve hot and enjoy!