炸酱面（zha2jiang4 mian4, “fried sauce noodles”), aka “noodles with fried bean sauce” is one of those dishes that I strongly associate with Beijing, though its origins lie in Shandong. Aficionados of Chinese cuisine would note that Beijing food (and all cooking in northeast China) is rooted in 鲁菜 (Lu3cai4 “Shandong cuisine”), one of the 8 great schools of Chinese cooking.
I’ve always loved proper 炸酱面 because the noodles are thick and chewy, and remind me of freshly made spätzle, while the freshly shredded cucumber and radish (or even more veggies if you get lucky) offset the rich and salty sauce.
Zhajiang mian is also a Korean dish (in a sense). Alternately called 자장면 짜장면 (jajangmyeon / jjajangmyeon), it is clear we are talking about the same dish linguistically. In culinary terms, Jajangmyeon is its own dish in Korea. The sweeter sauce is full of onions and seafood (instead of just salty beans and pork scraps).
As a certain podcast host would say, always read the plaque. Interestingly enough, Incheon claims Jajangmyeon as one of its specialties, though it gives credit to the influx of Chinese workers in 1884. Apparently, they would make the sauce in China and carry it across on merchant ships, serving it on freshly made noodles.