Chow mein sandwich consists of crunchy noodles and ground pork which are soaked in thick gravy and sandwiched between two halves of a hamburger bun. The gravy is typically made with bean sprouts, onions, and celery.
The sandwich originates from Fall River, Massachusetts. It was invented in the 1920s by Frederick Wong, a Cantonese immigrant, who originally sold it to immigrants from England, Ireland, and Canada who'd come to the state to work in textile factories.