Poaching the shrimp with Old Bay seasoning before pickling with cider vinegar, lemon juice, and aromatics is the key to this flavorful appetizer.
In a medium pot, bring 2 quarts water, Old Bay, bay leaf, and 1 tablespoon salt to a boil. Reduce heat; simmer 10 minutes. Add shrimp and cook until just pink and opaque, 30 seconds; drain.
Stir together shrimp and remaining ingredients in a bowl. Transfer mixture to a container. Cover tightly; shake to distribute. Chill at least 5 hours and up to 2 days before serving.