This is not exactly a restaurant tip but a gastronomic curiosity.
Baelo Claudia was once famous for its fish sauce called Garum, which was really famous in all the roman empire, and appreciated as nowadays caviar.
It was made out of the parts of the fish they wouldn't it (head, tails...) in some stone bassins that you can still see if you visit the ruins.
At the beach shore there are a few little restaurants (chiringuitos) where you can have a nice meal (fixed menu or a la carte), some tapas or just a few beers. They are open only in summer I think.
Favorite Dish: "Zanahorias aliñadas" (carrot salad with garlic and olive oil)
Atun encebollado (tuna fish with onion)