If using raw shrimp, blanch them in boiling water for 2 minutes until pink, then immediately plunge into an ice bath; if using pre-cooked, simply peel and devein.
Dice the shrimp into bite-sized half-inch pieces and place them in a large glass mixing bowl.
Finely dice the red onion, cucumber, roma tomato, and jalapeño, removing the seeds from the jalapeño if you prefer less heat.
In a small jar, whisk together the lime juice, chili powder, sea salt, and black pepper to create the marinade.
Pour the lime dressing over the shrimp and vegetables, tossing gently to ensure everything is well-coated.
Cover and refrigerate for at least 15 minutes to allow the flavors to meld and the shrimp to absorb the citrus.
Just before serving, gently fold in the diced avocado and chopped fresh cilantro to maintain their vibrant color and texture.