Bring a pot of salted water to a boil and poach the shrimp for 2-3 minutes until pink and opaque.
Immediately transfer the shrimp to an ice bath to stop the cooking process, then drain 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.
Add the chopped shrimp, finely diced red onion, and minced jalapeño to the bowl, tossing to coat thoroughly.
Fold in the diced cucumber, tomato, and fresh cilantro, allowing the flavors to meld in the refrigerator for at least 15 minutes.
Just before serving, gently fold in the diced avocado to maintain its creamy texture and prevent browning.