We ate here twice during our stay in Lisbon and really enjoyed both visits. The restaurant consists of indoor and outdoor tables, with buffet food set out indoors (there is an a la carte menu for the evenings.) The lunchtime buffet costs around 8 euros, or 10 with a homemade fruit juice (the fruit juice option is well worth it and tasted excellent both times.)
When we arrived we asked the staff which dishes were vegan, and they took us through these both times having asked the chef. Given that they write notes beside each dish to explain what it is I'm not sure why they don't also write whether they are vegan on these to save themselves time, but in any case each time there were only 1 or 2 non-vegan dishes (out of around 12) so there was plenty of choice. This included Tofu croquettes, a seitan stew, vegetable stuffed tacos, noodles, rice, salad etc - more than enough to cram a plate full of different foods.
The service wasn't outstanding - not unfriendly but not exactly engaging, but otherwise we enjoyed our visit enough to come back a second time and will do so again when we are back in Lisbon.