Mediterranean Fish in Zucchini Jackets

Adapted from a dish served at a country restaurant near Valencia, this zucchini-wrapped fish with a black olive vinaigrette is as virtuous as it is delicious. And it’s easy, to boot. In Valencia, it’s made with the firm-fleshed pez limón (a kind of amberjack), but many other fish—sea bass, pompano, sole—work well in this preparation. Choose the longest zucchini you can find, so that the slices can wrap comfortably around the fish fillets.