1. Make the dressing: Whisk together all ingredients in a bowl.

2. Make the salad: Bring a pot of water to a boil. Prepare an ice-water bath. Using a kitchen mallet, pound both sides of calamari bodies a few times to tenderize. Insert a sharp knife into calamari bodies, cut along seam, and then open like a book. Lightly score inner sides at 1/4-inch intervals. Cut in half lengthwise to form 2 pieces, then slice into triangles, each about 4 inches tall by 1 1/2 inches wide. (Leave tentacles whole, or halve if large.)

3. Blanch calamari in boiling water for 30 seconds. Using a slotted spoon, transfer to ice-water bath to stop the cooking. Drain, and pat dry. Place calamari in a nonreactive bowl.

4. Put cockles into a saucepan, and cover with water by 1 inch. Cover, and simmer, until shells open, about 7 minutes. Drain; discard any unopened shells.

5. Add cockles, watermelon, scallions, cilantro, mint, chile, pickled onion, and dressing to calamari, and toss to combine. Garnish with cilantro and mint.