I had the best Southeast Asia meal here in Buenos Aires last week. It's in a restaurant that's called "Cocina Sunae"
This is a "behind the closed doors" kind of restaurant which means it is located in the Chef's house. It's not very big but the atmosphere, the food and the service was amazing! They are open from 8pm on Thursday, Friday and Saturday only. You need to order your entree choice at time of reservation. The cost is 150 ARG peso for a 4 course meal and the price includes water and tea. They have a different menu every week. I will definitely go back there again before i leave Buenos Aires. Here's their website: http://www.cocinasunae.com