The Copacabana in front of the Tropical Hotel is recommended. Good seafood. Cold beer and wines. Picturesque settings. You'll find your NGO guys/ladies from all over the world there!
The Restaurant of Tropical Hotel is also good, but less choices than the Copacabana.
Avoid the Girassol hotel restaurant at all costs! The food there is warmed up and it's a festival of soggy fries in glassy sauces. Despite the referred unforseen, Girassol hotel restaurant still is one of the best restaurants in town, with a good breakfast, sunday lunch and dessert buffet. Definetelly shouldn't be avoid it!
The Sporting is a good place to eat if it's not raining: nice tables set outside and separated by neat little hedges. Great place to watch sport events on a telly.