The beauty of most Asian cuisines, and no less so Vietnamese, is that most things can be cooked very quickly. So, fast food in Vietnam is not junk food, unlike the situation in Australia and most Western countries. The most popular Vietnamese dish is pho ba (pronounced like "fur" but with a shorter duration to the syllable, and bah, as a long syllable). It is a soup of white rice noodles, beef pieces, been sprouts, leafy greens, basil, herbs and freshly squeezed lime juice, all in a light beef or chicken broth. Pho ga is the chicken version.
Pho is ubiquitous in Vietnam and is eaten at any time of the day, most usually, though, for breakfast or lunch. It takes three minutes to make and serve and is freshly made for each order. Only the broth has been prepared beforehand. The noodles are soft and cook when they are dropped into the hot broth for one minute. The beef is thinly cut and is cooked after two minutes in the broth. Tourists and locals all lap it up and it is surprisingly filling. It's also healthy. There is no need to look for junk fast food in Vietnam — there is no need anywhere, but some people don't know any better. There are shops that specialise in just pho, and many street food stands serve up huge quantities of it. Many tourists and imbibers swear as to its restorative properties after a night on the tiles.