Bring a small pot of water to a boil and poach the shrimp for 2 minutes until pink and opaque, then immediately transfer to an ice bath.
Once cooled, peel and devein the shrimp if necessary, then chop into bite-sized pieces and place in a glass bowl.
Pour the lime juice and lemon juice over the shrimp, ensuring they are fully submerged, and let sit for 10 minutes.
Finely dice the red onion, cucumber, tomato, and jalapeño, ensuring all seeds are removed from the jalapeño for a milder heat.
Add the diced vegetables and minced fresh cilantro to the shrimp mixture and stir gently to combine.
Carefully fold in the cubed avocado just before serving to keep the pieces intact and creamy.
Season with sea salt and black pepper, then serve immediately in chilled bowls.