Chop suey (the name of the dish) comes from Chniese for "assorted stuff" (mixed organ parts and whatever, though the American version was Americanised). In modern Romanisations, zasui (Mandarin) and zaapseoi (Cantonese). Sounds very similar to Korean chapchae, http://en.wikipedia.org/wiki/Japchae so I look at the Chinese characters, and it's close (not the same; "assorted parts" looks to have mutated into "assorted vegetables"). Chapchae having about the same antiquity as jjajangmyeon (approx 100 years), one can wonder about the origin - might it even be an American import?