The signature red sauce?

Do a quick google search for the foe yong hai famous in the Netherlands, and one of the most recognizable aspects is undoubtedly the red sauce served with the egg omelet.

In Chinese-Indonesian restaurants in the Netherlands this dish is often served with a sweet and sour tomato sauce. It consists of a mix of tomato paste, flour, oil, sugar, and salt. In Indonesia, the dish also exists as part of Chinese-Indonesian cuisine as an omelet.

Eggs foo young in the United States can also be served with a brown gravy. Foe yong hai has proven itself to be a very adaptable dish. In Missouri, USA, for instance, the dish even found itself between two slices of bread, becoming an egg foo young sandwich called St. Paul sandwich. This sandwich was likely made up to suit American tastes.Becky Mercuri, American Sandwich (2009): 71