Place chopped onion in a colander, and rinse with cold water. Drain.
Bring 6 cups water and 1/4 cup juice to a boil in a Dutch oven. Add shrimp; cook 3 minutes or until done. Drain and rinse with cold water; peel shrimp. Combine shrimp and 1/2 cup juice in a large bowl; cover and chill 1 hour. Stir in onion, cucumber, and remaining ingredients. Serve immediately or chilled.