Much of what I tell you will be unknown and unfamiliar with the younger generations in Vietnam. They cannot imagine their ancestors once lived like that.
The Vietnamese of yesteryear of course were very poor, just like Koreans.
If Koreans survived on kimchi and rice, Vietnamese, well, survived daily on rice, dưa chua (fermenter sour cabbage), cà (fermented eggplants), tương (mung bean soy sauce).
For proteins, they mostly get from peanuts and mung beans (Vietnamese normally are not keen on red beans).
The more fortunate could eat dried fish.
They could also catch raw fish, shrimp, eel, frogs which were plentiful. But most of those produce would be sold in the market to provide extra income for the family or to help them pay tax, the most burdensome for peasants.
People along the coast of course had access to fish caught.
During Lunar New Year (Tết) or other special or festive occasions, they could eat a little of PORK and CHICKEN. These were the two most popular meat available to them during those special celebrations.
And of course, they ate dogs.
Beef and even buffalo meats were almost unheard of. Simply because they were beasts of burden. And it was extremely rare to kill them just for the meat.