The seafood along the harbour is the obvious draw — the restaurants buy direct from the fishing boats, so what you eat is what was caught that morning. Tasca El Puerto, on the harbourside, does plain grilled local fish (vieja, sama, cherne) with mojo verde and papas arrugadas. El Bote is a step up in price and ambition, with a daily menu based on the catch.
Away from the harbour, the village restaurants serve the standard Canarian repertoire — rabbit in salmorejo, ropa vieja, carne fiesta. Look for places with a chalkboard menu and locals at the bar; the tourist-trap places further south have not yet colonised San Juan.