Combine first 4 ingredients in a large skillet; bring to a boil. Add shrimp and scallops; cover, reduce heat, and simmer 4 minutes or until done. Drain.
Combine shrimp, scallops, and onion in a large bowl. Combine orange rind and next 7 ingredients (orange rind through salt) in a small bowl; stir well. Pour 1/4 cup orange juice mixture over shrimp mixture; toss well, cover, and chill 30 minutes. Cover and chill remaining orange juice mixture.
Add spinach, orange sections, and cucumber to shrimp mixture; pour remaining orange juice mixture over salad, and toss well.