If you're on the island of Oléron do not hesitate to try one of the specialities of the region: the oysters. This area is well know for its incredibly delicious fish and seafood! If you want to try these specialities I'd recommend going to Saveurs des iles, a charming place where they've reinvented French cuisine to give it a sophisticated look without losing the quality of home cooking. Make sure you ask for some seafood, you won't regret it!
If you want to try a good meal made from produce local to Oléron Island, get yourself down to the hotel-restaurant L'Ecailler and make sure nothing is left on your plate. The food made here is made following the traditional recipes from the Poitou-Charentes region. Affordable prices, and the food is of a high standard. The restaurant is located right on the harbour of the town. Don't leave without tasting the sweet desserts at L'Ecailler!