Combine water and 1/4 cub salt in a large saucepan
bring to a boil over high heat.
add shrimp and immediately turn off the heat. Let the shrimp sit until just cooked throuigh, about 3 minutes. Transfer to a cutting board until cool enough to handle, about 10 minutes.
Chop shrimp into 1/2 inch pieces and place in a medium noreactive bowl.
Add lemon juice, lim and orange juice.
Stir in cucumber, onion and chiles.
Refrigerate 1 hour
Stir tomato, avocado, chopped cilantro, oil and 1/4 tsp. salt into shrimp mixture.
Let stand at room temperature for 30 minutes before serving.
Garnish with cilantro leaves, if desired