This restaurant's located just outside of the first ring road, between avenues Melchor Pinto and Ballivian, and is easy to miss if you're not looking.
The food was quite good, and I went here three times for lunch during my time in Santa Cruz. Like most buffets in Santa Cruz, it's best to arrive earlier rather than later as the food can go quickly and the heating tables are somewhat lacking. However, this is the same at most restaurants of this type.
There was a large variety of vegan friendly and vegetarian food, as well as good empanadas and various fried foods. The large majority of food was vegan friendly, though on my third visit I did encounter something that was certainly meat, so do watch out. However, be careful as the soy protein common in Bolivia is very hard to tell from real meat when cooked with fats--sounds like other reviewers made this mistake. The key is in the shape and slight soy taste.
The owners were very kind and friendly, but not too talkative as to keep you waiting.
One thing to think about is bringing your own drink, because this restaurant only serves juices, something I'm hesitant to drink in Bolivia.
Cons: Real meat is sometimes served (rare), Bring your own drink