Sauté the onion and tomato for a few minutes
Put-in the Salmon heads and let each side cook for 3 minutes
Add water and bring to a boil. Let this simmer for 10 minutes
Add the sinigang sa Sampaloc mix and let this simmer for 5 minutes
Add the fish sauce followed by the spinach
Turn of the heat and cover the pan for 5 to 7 minutes
Serve hot. Enjoy!