No evening during our stay in Luang Prabang went without visiting this place. The food is very simple but tastes delicious when you add some of the sauces provided on the tables. At the end of the day, you can't complain about anything when the place makes you full for 10 000 kip.
There are quite a few stalls on the same market street that sell sandwiches. Vegetable-only version is vegan if you skip mayonnaise. Same is with juice shake stalls. Tell them not to add any milk and you have a nice vegan dessert. Be aware that coconut milk powder that they offer instead of milk is NOT vegan (contains casein).
Cons: could be cleaner