Cook shrimp in boiling water 1 minute, or just until shrimp turn pink. Drain and plunge into ice water until chilled; drain.
Stir together vermouth (if desired) and next seven ingredients in a medium bowl. Add shrimp, tossing gently. Spoon ½ cup shrimp mixture into each of 4 martini glasses. Garnish, if desired.
Makes 4 servings.
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