Thaw shrimp, if frozen. Finely shred 1 teaspoon orange peel; set orange peel aside. Peel and section oranges over a bowl to catch juices; set orange sections aside. Measure juices and add additional orange juice to equal 1/3 cup; set orange juice aside.
Rinse shrimp; pat dry with paper towels. Cook shrimp in boiling, salted water for 1 to 3 minutes or until shrimp turn opaque; drain. Rinse with cold water; drain again. Set shrimp aside.
For dressing, in a small saucepan bring reserved orange juice and rosemary to boiling. Remove from heat; stir in reserved orange peel, vinegar, and salad oil.
In a large bowl toss together spinach, onion rings, orange sections, and shrimp. Pour dressing over salad. Toss lightly to coat. Makes 4 servings.