I lived in Lisbon for 2 years. I've been to almost all restaurants in town. From the Cheap trash in Mouraria to the Fancy ones in the Av. da Liberdade. Cantinho is far, I mean, far away the best food experience in Lisbon.
What to order (not in the same day, cause the dishes are always for 2)
1Pataniscas de Bacalhau com arroz de tomate (fried cod fish muffins with tomato rice)
2Gambas ao Alho (shrimp in moustard and garlic sauce)
The chocolate cake.
ps: it's a very tiny place with a few tables and doesn't accept reservations. So if you wanna eat there, go with one or two more people I get there early!