2 pounds cleaned squid
Heaping 1/3 cup niçoise olives, finely chopped
1/3 cup finely chopped celery
1/3 cup chopped celery leaves
1/3 cup thinly sliced scallion
1 teaspoon grated lemon zest
1/4 cup extra-virgin olive oil
Rinse squid under cold running water, then pat dry between paper towels.
Halve tentacles lengthwise and cut bodies (including flaps, if attached) crosswise into 1/8-inch-wide rings.
Cook in a 4-quart pot of boiling salted water (1 tablespoon salt for 3 quarts water), uncovered, until just opaque, 30 to 40 seconds.
Drain and immediately transfer to an ice bath to stop cooking.
When squid is cool, drain and pat dry.
Meanwhile, combine remaining ingredients and 1/4 teaspoon salt in a large bowl.
Add squid and toss until combined well.
Serve chilled or at room temperature.