Preheat a skillet/wok with cooking oil. Saute the onions until they are soft. Add the tomatoes and chili (if using) and continue to cook until the tomatoes are soft
Add in the sardines, be careful not to stir too much and break the fish into pieces. Season with more salt to your taste if needed. Bring to a gentle simmer and then turn off the heat
Sprinkle with chopped green onion and voila…dinner is ready