Food in Huacachina is not its strong suit. The dozen or so restaurants ringing the lagoon are aimed at tourists, prices are higher than in Ica, and quality is mixed. Expect pizza, pasta, basic Peruvian standards (lomo saltado, ceviche, arroz con pollo), burgers, and milkshakes. The ceviche is workable but you are a long way from the coast — eat it in Lima or Paracas if you have the choice.
For a better meal, take a 10-minute taxi back into Ica, where there are good casual restaurants on the central plaza and around Calle Lima. The local specialty worth trying is tejas — small sweets made from manjar blanco wrapped in fondant — and the dessert wines and pisco produced at the bodegas (vineyards) around Ica.