La Font de Gall, just behing the square in Pollensa, is very nice for a casual lunch. They have great desserts as well.
Il Giardino on the square in Pollensa is also excellent. It is a bit more formal than La Font de Gall but still quite casual, particularly at lunch time.
If you want something quite informal the Cafe Illa is good for simple pa amb oli and a nice glass of wine or cool beer.