We visited Prana, on the main street of Chaltén toward the back of town, twice for dinner at around 8:30/9:00 pm in the summer, peak tourist season. This is the busiest time of the day and year and it was clearly overwhelming for a small, laid-back restaurant. The staff were stressed out in the tiny kitchen trying to serve people at their ~6 tables and service really deteriorated, with even simple drinks taking 30 minutes to get to the table. They were apologetic, but I'd definitely recommend going at an off-peak time if possible to have a better experience.
Although the price on HappyCow is listed as "expensive", prices here are in line with other restaurants in Chaltén (being an isolated place, everything is rather expensive), with a main dish approx $10 USD. In addition to mains like lasagna, risotto, curry, they also have small plates like salad, crepes, bruschetta, as well as teas, fresh juices, beer including some artesanal, and even a mojito. They also have a few baked goods and desserts and I enjoyed a rare vegan dessert!!
It's definitely a pleasure to find a vegetarian restaurant with lots of vegan options with a pleasant hippie vibe in rural Argentina. Chaltén is a uniquely veg-friendly town for the area because of the type of travelers who visit. The food at Prana was fine in quality and quantity. I was disappointed we didn't want to go back because the service was such a letdown, but I'm sure it would be a good experience at non-peak hours.
Cons: Small place gets overwhelmed, Not economical for regular meals