10 cups water
3 tablespoons plus 1/4 teaspoon kosher salt, divided, plus more to taste
8 ounces small to medium scallops
8 ounces peeled and deveined raw medium to large shrimp
8 ounces boneless, skinless swordfish or other firm, meaty fish, cut into 1/2-inch pieces
3 celery stalks, finely chopped
1 large shallot, finely chopped
1/4 cup finely chopped fresh flat-leaf parsley
1/4 cup extra-virgin olive oil, plus more to taste
3 tablespoons fresh lemon juice, plus more to taste
1/4 teaspoon black pepper, plus more to taste
1/8 teaspoon crushed red pepper (optional) Butter lettuce or radicchio leaves and lemon wedges, for serving

Step 1
Fill a large bowl with ice water; set aside. Bring 10 cups water to a boil in a large saucepan over medium-high. Reduce heat to medium, and stir in 3 tablespoons salt. Working in batches, add scallops, shrimp, and fish to boiling water; cook to desired degree of doneness (45 seconds to 1 minute and 30 seconds for scallops, depending on size; 1 to 2 minutes for shrimp; 2 to 3 minutes for swordfish). Using a slotted spoon, transfer cooked seafood to prepared ice water; let stand 30 seconds to 1 minute. Transfer to a colander; drain well, and transfer to a medium bowl.

Step 2
Add celery, shallot, parsley, oil, lemon juice, black pepper, crushed red pepper (if using), and remaining 1/4 teaspoon salt to seafood mixture; gently stir just until combined. Let stand at room temperature 5 minutes. Add additional salt, oil, lemon juice, or black pepper to taste. Serve seafood salad with lettuce or radicchio and lemon wedges.

Make Ahead
Seafood can be cooked up to 1 day ahead and stored in an airtight container in refrigerator.

By MARY-FRANCES HECK