[I went there on March 2015 and the price for the set menu was of 15Bs. The hours were Monday-Saturday 12:00-14:00. The name is FREYA]
I went there late March 2015. The restaurant seems to be also a fitness centre, and the place is dark. The menu included a starter (salad buffet), a soup, a main course, a drink and a dessert. The day I went I had an oats soup (sopa de avena), the chinese rice (arroz chino)*, a soy drink and a peach in syrup. All of it was kind of tasteless.
There is a 'comedor vegetariano' (with no name) located at one block (calle Loa #621, between Arenales and Ayacucho/Estudiantes) for the same price (15Bs, for a soup, a main course, bread and mate), so maybe if the set menu doesn't sound appealing you may check this other restaurant.
*I asked if the rice was vegan and they told me yes, but in fact it contained eggs, so if you're vegan check twice before ordering.
Cons: Not vegan-friendly, Very basic and flavourless