We ate at The Food Temple with my partner two times within one week in June, just after it had had a very positive review on Time Out Lisboa. Both times we shared the three tapas of the day, one main course, and two desserts. The second time we also shared a soup of the day. Together with a bottle of wine, the bill was around 40 euros both times.
The food was excellent. However, if you're after huge portions and lots of protein, this is the wrong place to go. Lisbon has plenty of good quality veggie buffet places for that. With the tapas, one main course, and the desserts, we weren't feeling stuffed, but definitely sated. If you have a hearty appetite, you'll probably want to eat a main course and at least a couple of tapas by yourself.
The main thing about the food here is that some serious thinking has gone into the design of the meals. Each portion had creative contrasts of textures, flavors and culinary traditions, and they were delightful. This is quite an accomplishment, given that the menu changes every few days.
You shouldn't go to the Food Temple without an advance booking. Both times we went there the place was completely full, and many people looking to eat there were turned away. The bookings were on the hour, last one being at 10 pm.
The milieu of the place is undoubtedly one of the best in any restaurant we've ever eaten. On a warm summer night, with the tables laid out on the small square in the heart of Mouraria, with the small set of stairs next to the tables serving as a "bar" for people queuing for a table, it indeed feels like a sacred amphitheatre of eating. It's worth going there just for the ambience, but I imagine it's rather different in the winter.
As for the service, criticized here by many, I think it was good, considering the place was completely full both times. Second time we ate there, there was one waiter who wasn't focused on his job, carrying dishes to wrong tables, and not remembering all of the day's dishes. Still, even he was very friendly. In any case, you should be prepared to spend about two hours there if you plan on eating all of the menu. It's not a place for rushed dinners.
After finishing our second dinner on a Sunday night, the place starting to close and the kitchen staff preparing to share a meal on one of the outdoor tables, we were thinking that rarely, if ever, we've had as pleasant a dining experience as that night. Eating at the Food Temple is essential for every vegan going to Lisbon.