Bring a small pot of water to a boil and blanch the shrimp for 60 seconds until just pink, then immediately plunge into an ice bath to stop the cooking.
Drain the shrimp thoroughly and chop into bite-sized pieces, then place them in a glass bowl.
Pour the lime juice and lemon juice over the shrimp, ensuring they are completely submerged, and refrigerate for 30 minutes.
While the shrimp marinates, dice the red onion, cucumber, and roma tomato into uniform pieces.
Finely mince the jalapeño and chop the fresh cilantro.
Remove the shrimp from the refrigerator and stir in the diced vegetables, jalapeño, and cilantro.
Gently fold in the diced avocado to maintain its shape and creamy texture.
Season with sea salt and black pepper, tossing lightly to combine before serving chilled.