Place the shrimp in boiling water for 2-3 minutes or until they are pink and no longer translucent (do not overcook or they will be rubbery and tough). Drain and plunge them into a bowl of ice water. Let them chill while you do the next step.
Chop the mango, cucumber(scrap out the seeds first), tomatoes(I use Roma), cilantro, and red onion. Drain and chop the shrimp. Place the all the ingredients in a bowl. Add salt to taste and the juice of the limes and toss.
Chill for about an hour and serve with tortilla chips or on tostada shells.