Bring a pot of water to a boil and poach the shrimp for 2-3 minutes until they are pink and opaque.
Immediately drain the shrimp and transfer them to an ice bath to stop the cooking process and keep them tender.
Once cooled, pat the shrimp dry with a paper towel and chop into bite-sized pieces.
In a large glass bowl, whisk together the lime juice, chili powder, sea salt, and black pepper to create the marinade.
Finely dice the red onion, cucumber, tomato, and jalapeño, then add them to the bowl with the lime mixture.
Stir in the chopped shrimp and fresh cilantro, tossing well to ensure everything is coated in the citrus dressing.
Cover and refrigerate for at least 15 minutes to allow the flavors to develop.
Just before serving, gently fold in the diced avocado to maintain its creamy texture and prevent browning.