Bring a pot of water to a boil and blanch the shrimp for 2 minutes until pink and opaque, then immediately plunge them into an ice bath to stop the cooking.
Once cooled, pat the shrimp dry and chop them into bite-sized pieces, placing them into a large glass mixing bowl.
In a small jar, whisk together the lime juice, olive oil, chili powder, sea salt, and black pepper to create the marinade.
Pour the marinade over the shrimp and toss well to ensure every piece is coated.
Finely dice the red onion, cucumber, tomato, and jalapeño, and roughly chop the cilantro; add all vegetables to the shrimp bowl.
Gently fold in the diced avocado just before serving to maintain its creamy texture and prevent mashing.
Let the ceviche sit in the refrigerator for 15 minutes to allow the citrus and spices to fully penetrate the ingredients.