Blanche shrimp in boiling water for 1-2 minutes, then place them immediately in ice cold water to shock them and stop the cooking (if cooked too long, shrimp will become tough). Strain when cooled.
Cut each shrimp in 3-4 small pieces and place in a glass mixing bowl. Pour the fresh squeezed lemon and lime juice over the shrimp and stir. Add red onion, bell pepper, cucumber, tomatoes and jalapeno and place in the refrigerator to marinate for about 2 hours.
Remove from the refrigerator and add the cilantro, then marinate for at least another 2 hours.
When you’re ready to serve, slice the avocados and arrange them on a plate. Add about a cup of the ceviche to each plate, being sure you strain out the excess juice first. You can serve more or less on each plate, depending upon whether you're serving it as an appetizer or main course.