If using raw shrimp, poach in boiling water for 2 minutes until pink, then immediately plunge into an ice bath to stop the cooking process.
Pat the chilled shrimp dry and cut into half-inch pieces, then place them in a large glass mixing bowl.
Finely dice the cucumber, Roma tomato, red onion, and jalapeño, ensuring you remove the seeds from the jalapeño for a milder heat.
Add the diced vegetables and chopped fresh cilantro to the bowl with the shrimp.
In a small jar or bowl, whisk together the lime juice, lemon juice, extra virgin olive oil, sea salt, and black pepper.
Pour the citrus marinade over the shrimp mixture and toss gently to ensure everything is evenly coated.
Cover and refrigerate for at least 30 minutes to allow the flavors to meld and the shrimp to absorb the bright citrus notes.
Just before serving, gently fold in the diced avocado to maintain its creamy texture and prevent it from mashing.