Heat oil in a pan and saute' onion until transparent. Add in tomatoes and cook until partly soft.
Add in the shrimps and let the flavor of the onion and tomatoes sip through. This is usually when the shrimps turned orange.
Add the optional ingredients and cook until they are soft. I if not using,move to the next step.
Let the Sinigang boil and add in the Sinigang Mix ( I use half of the mix,it depends on you)
Season with fish sauce or salt.
The Sinigang product should be gently sour and balance with the salty season of the fish sauce or salt.
Turn off heat and put the Spinach and green onion on top. Let it sit for a few minutes before serving.SERVE HOT AND ENJOY!