Place the scallops in a large metal or heatproof glass bowl. In a medium saucepan, bring 4 cups water to a boil. Add the halved lemon, bay leaf, peppercorns and 2 tbsp. salt; return to a boil, then pour the mixture over the scallops. Allow to sit until the scallops are just opaque in the center, about 3 minutes. Transfer the scallops to a small bowl, discarding the brine mixture. Cover the scallops and refrigerate until cool.
In a medium bowl, mix the scallops, shrimp, onion, celery and leaves, parsley, chile and thyme with 1/2 cup EVOO and the lemon juice. Season to taste with kosher salt and black pepper.
Divide among 4 bowls. Drizzle with more EVOO and serve with the lemon wedges.