Bring 6 cups water to a boil; add shrimp, and cook 3 to 5 minutes or just until shrimp turn pink. Drain and rinse with cold water. Chill 30 minutes.
Peel shrimp, leaving tails on, and devein, if desired.
Toss together shrimp and next 3 ingredients.
Combine oil through ground pepper in a jar; cover tightly, and shake vigorously. Pour 1/2 cup mixture over shrimp mixture, reserving remainder; toss gently. Cover and chill 30 minutes.
Serve shrimp mixture on greens; top with cilantro sprig, if desired. Serve with reserved dressing.