It’s one of the best value ways to eat well on the island. A menu del dia is a fixed-price lunch menu, usually three courses (starter, main and dessert), often with bread and a drink included, and it’s offered at most traditional restaurants, not just the tourist spots.
Expect to pay somewhere between 9.50 and 15 euros depending on the place, a fraction of what the same courses would cost ordered a la carte in the evening.
It’s a lunchtime tradition specifically, typically served from around 1pm for a couple of hours, and it runs all year round rather than just in season. It’s popular with locals on their lunch break as much as with visitors, so ordering one is also a good way to eat where islanders actually eat.