Peel and devein shrimp, leaving tails intact. Bring water to a boil in a small saucepan. Add shrimp and scallops; cook 2 minutes or until shrimp turns pink. Drain well, and set aside.
Combine vinegar and next 5 ingredients in a small heavy-duty, zip-top plastic bag; add shrimp and scallops. Seal bag, and shake until seafood is well coated. Marinate in refrigerator 1 hour, turning bag occasionally.
Remove seafood from marinade, reserving marinade. Place 1/2 cup spinach on each serving plate. Arrange shrimp and scallops evenly on spinach. Drizzle with marinade.