Haven't been in a very long time, so I wouldn't be able to recommend specific places, but I can recommend specific dish.
Turmeric fish (Chả Cá Lã Vọng). This is a specialty and you can find places that only do that. There's a pan in front of you with some oil, and you put fish and dill and tumeric and cook it yourself.
DIY Fruit smoothies (Hoa Qua Dam). You can find that in the streets. They give you these cups with fruits and ice and condensed milk and you're supposed to blend everything yourself by hammering the content with your spoon. So good!