Pour the water into a pot and add a teaspoon of salt to the water. Bring to a boil over medium heat, once it breaks the boil remove from the heat.
Ladle the shrimp into the boiling-hot water. Once the shrimp has turned pink remove immediately from the water and spread on a tray to cool down.
Mix the lime and orange juice.
When the shrimp has reached room temperature place on a large plastic, ceramic or glass container. Pour the mix of lime and orange juice onto the shrimp, covering them.
Cover the container and let the shrimp rest in the fridge for half an hour.
Add onion and pepper strips to the shrimp, cover and return for the fridge for another half an hour.
Pour the shrimp into a sieve to remove as much of the juices as possible (throw away the juices). Taste, and if you find the taste too acidic, rinse quickly with a cup of ice water.
Mix the shrimp with the mango. Season with salt to taste. Keep refrigerated until it's time to serve.
Arrange the lettuce on a platter and serve the shrimp mixture on it. Drizzle with the olive oil.