There are three of these appealingly-decorated restaurants around town: this one in Vieille Ville, as well as one on Rue Lissignol in Centre Ville Rive Droite and one in the International Area. The idea is basic: lunch and dinner, you get half a roast chicken, Provençal-style potatoes, and green salad for 14.90 SF. Sauce for the chicken is optional (and a bit extra), and they serve a few salads as mains in the same price area. But otherwise that's it, except for desserts.
Chez Ma Cousine is understandably popular, not only because the food's cheap and good, but also because sitting outside in the Vielle Ville and International Area is great for people-watching.