Bring a pot of water to a boil and blanch the shrimp for 2 minutes until pink and opaque, then immediately transfer to an ice bath.
Once cooled, peel and devein the shrimp, then chop into bite-sized half-inch pieces.
In a large glass bowl, whisk together the lime juice, extra virgin olive oil, sea salt, black pepper, and garlic powder.
Add the chopped shrimp to the lime mixture, tossing well to ensure every piece is coated, and let marinate in the refrigerator for 15 minutes.
Finely dice the cucumber, roma tomato, red onion, and jalapeño, and chop the fresh cilantro.
Remove the shrimp from the fridge and fold in the diced vegetables and cilantro.
Just before serving, gently fold in the diced avocado to maintain its creamy texture and prevent mashing.
Serve chilled in a bowl or over a bed of mixed greens.