Formerly only famed for offering local dishes, Hanoi is getting more and more involved to serve food from across Vietnam and I really like it this way!
Some years ago you just could find some basic Hanoian dishes in local kitchens and of course foreign restaurants. Conservative as the Capital has been this changed now over the years and the advantages of diverse menues has been adopted by many. Nowadays you can start your street food adventure by digging in some delicious bowl of banh da cua (a dish from Haiphong with freshwater paddy crab). May you follow up with Anchovy-dipped banh canh Trang Bang or even bun bo from Hue.
After work most of office workers are crowding into one of the street food stalls under lines of dim light bulbs strung into the trees and slurp hungrily on spicy noodles washed down with iced tea or even better a refreshing bia hoi (fresh beer).
You might consider to finish your adventure with banh canh Trang Bang a kind of medicinal dish with a lot of fresh herbs.