This new-ish spot was also recommended to me by the family who runs Paraiso. Recently opened, the owner/manager is a young guy named Fernando who is very friendly and will explain what they have. They also make soy milk, cheese, and tofu. Similar to Paraiso, this is a Seventh Day Adventist-type restaurant (and thus closed on Saturdays); it's a bit more overt here, though. They are also very sparing on the salt and spices, but salt available on the side.
Have had some delicious soups here, but since it's a smaller and more out of the way, they don't always have everything on the menu - you can request something and they'll have it for you the next day. It's not really hard to find at all, I made sure the map marker was correct... just 5 blocks or so from the Plaza de Armas. Not open evenings. Set menu is cheap at 5 soles. Recommended!
Cons: slightly hard to find, some items a bit bland, not open nights