Jinju Hoegwan
Bean noodles!
The place is popular with office workers in the area in the summer and expect long lines, but if you go outside of regular rush lunch hours you can easily get a seat.
Jinju Hoegwan has been around for over 50 years and is a landmark in the area right behind the old Samsung HQ.
For more info: +82-2-753-5388 (No English)
Opening hours: 10:30-21:00