Sri Lankan rice and curry is a different animal from the Indian version: a mound of red or white rice surrounded by five or six small dishes — a dhal, a coconut sambol, a fried vegetable, a fish or meat curry, and a green leaf sautéed with mustard seeds — served all at once so you can mix and match. In Unawatuna, every guesthouse serves it for breakfast (with a fried egg added to the usual lineup), and a handful of small local restaurants serve it at lunch for a few hundred rupees a plate.
The best value is usually at the smaller local places set back from the beach road, where the clientele is Sri Lankan and the food is cooked to a Sinhalese standard rather than adjusted for tourist palates. Ask your guesthouse owner where they eat; the answer is almost always somewhere that doesn't appear on TripAdvisor.