Broadway has been called “the Main Stem” since at least the early 1900s. The Broadway nickname of “Chow Mein Stem” (chow mein + main stem) reflects a time when chow mein restaurants were numerous along the big street.
 
“Chow Mein Stem” has been cited in print since at least 1928. Mott Street, in Manhattan’s Chnatown, also had the same “Chow Mein Stem” nickname. The term is of historical interest today.
 
A Broadway nickname similar to “Chow Mein Stem” is “Chow Mein Street” (cited in print since at least 1921, and in reference to Broadway by at least 1928).
 
 
Wikipedia: Broadway (Manhattan)
Broadway /ˈbrɔːdweɪ/ is a road in the U.S. state of New York. Perhaps best known for the portion that runs through the borough of Manhattan in New York City, it actually runs 13 mi (21 km) through Manhattan and 2 mi (3.2 km) through the Bronx, exiting north from the city to run an additional 18 mi (29 km) through the municipalities of Yonkers, Hastings-On-Hudson, Dobbs Ferry, Irvington, and Tarrytown, and terminating north of Sleepy Hollow in Westchester County.
 
12 April 1928, Life magazine, “Along the Main Stem” by Walter Winchell, pg. 16, col. 3:
And Broadway, frequently called “The Main Stem,” has so many Chinese restaurants that it is now tagged “The Chow Mein Stem.”
 
Google Books
14 June 1928, Life magazine, “Along the Main Stem” by Walter Winchell, pg. 10:
I’ve discovered other nicknames for parts of town. Broadway is known as Orange Juice Gulch, Mazda Lane, Coffee Pot Canyon, Fraudway and Chow Mein Stem. Then there’s the Thumping Thirties, the Flaming Forties, the Four-flushing Fifties, the Sexy Sixties, the Salacious Seventies, the Elegant Eighties and the Nancy Nineties.
 
Google Books
Broadway Portraits
By Samuel Marx
New York, NY: Donald Flamm
1929
Pg. 5:
You may have never heard the name of some of them. But they are part, particle and parcel of New York’s Main Stem, Hardened Artery, Great White Way, Incandescent Lane, Mazda Boulevard, Chow Mein Stem, Double Cross-Roads of the World, Two-Times Square, or, as somebody once called it, Broadway.
 
29 July 1930, Evansville (IN) Courier, “Walter Winchell On Broadway,” pg. 4, col. 6:
Abel Green first referred to Broadway as “Mazda Lane,” while others call it “Orange Juice Gulch,” “The Tungsten Belt,” “The Chow Mein Stem,” ‘The Big Artery” or “Coffee Pot Canyon.”
 
Brooklyn Newsstand
31 December 1937, Brooklyn (NY) Daily Eagle, “Broadway Newsreel” by Hy Gardner, pg. 6, col. 1:
And if many more Chinese restaurants open on Broadway, Vince Burnett suggests changing Broadway to the “Chow Mein Stem” .
 
Old Fulton NY Post Cards
23 July 1942, Philadelphia (PA) Inquirer, “Walter Winchell On Broadway,” pg. 14, col. 7:
Chinatown’s chow-mein stem, Mott st., which wasn’t named for a Chinese—but for a butcher by the name of Joseph Mott.