If using raw shrimp, blanch them in boiling water for 2 minutes until pink and opaque, then immediately plunge into an ice bath to stop the cooking process.
Peel, devein, and chop the cooked shrimp into bite-sized half-inch pieces.
In a large glass bowl, combine the lime juice, lemon juice, sea salt, black pepper, and extra virgin olive oil.
Add the chopped shrimp to the citrus marinade and toss well to coat; let it sit for 10 minutes in the refrigerator.
While the shrimp marinates, dice the cucumber, red onion, and Roma tomato into uniform small pieces.
Finely chop the fresh cilantro and dice the avocado into half-inch cubes.
Remove the shrimp from the refrigerator and gently fold in the cucumber, onion, tomato, cilantro, and avocado.
Taste and adjust seasoning if necessary, then serve immediately in a chilled bowl for maximum freshness.