Combine orange juice concentrate and next 4 ingredients in a large heavy-duty, zip-top plastic bag; add shrimp and scallops.
Seal bag, and shake until seafood is well coated.
Marinate in refrigerator 30 minutes, turning bag occasionally.
Remove shrimp and scallops from marinade, discarding marinade.
Coat rack of a broiler pan with cooking spray.
Place shrimp and scallops on rack; broil 5 1/2 inches from heat (with electric oven door partially opened) 4 minutes or until done.
Place 1/2 cup spinach on each individual serving plate.
Arrange shrimp and scallops on spinach.