While the literal translation of 炸醬麵 (zhà jiàng miàn) is "fried sauce noodles", perhaps a more useful one would be "noodles with meat sauce". Other translations I've seen include "noodles Peking style" (at Le Wei Xiang) and "Beijing pork noodles" (at Baozi Inn, whose version is pictured above). It's a simple dish of plain noodles topped with a rich sauce based on pork mince fried with one or more types of bean sauce. It's usually presented as shown above, with the sauce and garnishes laid out neatly on top of the noodles, and you mix it all up together before eating it.
The observant may note that this bears some resemblance to the Western spaghetti bolognese and the Korean ja jang myeon. Indeed, ja jang myeon is descended from 炸醬麵. Similarly, just as a simplified version of spaghetti bolognese is a popular student dish, so is 炸醬麵 — it's quick to make, uses inexpensive ingredients, and can be customised to suit the ingredients you have on hand.
While as mentioned above "noodles with meat sauce" is a reasonable translation, another possible option would be "noodles with bean sauce", due to the thick bean-based sauces used to give flavour and body. Sunflower's 炸醬麵 recipe uses sweet bean paste (甜麵醬/tián miàn jiàng) and chilli bean paste (豆瓣醬/dòu bàn jiàng), while the 炸醬麵 recipe at Tigers & Strawberries adds a third sauce, described as "soy bean sauce" — the author tells me via email that this is similar to yellow bean sauce (黃醬/huáng jiàng). Hoisin sauce (海鮮醬/hǎi xiān jiàng) could also be used as a secondary flavouring. The 3 Hungry Tummies version includes Sichuan pepper, too, for extra bite.
Although the noodles and sauce alone make a perfectly good dish, for me the important finishing touch is the vegetable "garnishes" which are mixed in with the sauce and noodles just before serving. These might include raw slivered carrots and cucumber, raw or lightly blanched beansprouts, blanched shredded cabbage, shredded thin omelette, and so on. (See also Beijing Haochi's description of perhaps the ultimate version of this.)
Recipes for 炸醬麵:
- 3 Hungry Tummies: Zha jiang mian 炸醬麵 noodles with Chinese mince sauce
- Red Cook: Zhajiang mian: a meat sauce taste test
- Sunflower Food Galore: Zha jiang mian 炸醬麵 — fried sauce noodles
- Tigers & Strawberries: Za jiang mein