Bring a medium pot of salted water to a boil and poach the shrimp for 2 minutes until just opaque.
Immediately transfer the shrimp to an ice bath to stop the cooking process, then drain and chop into bite-sized pieces.
Finely dice the red onion, cucumber, and jalapeño, ensuring the jalapeño seeds are removed if less heat is desired.
In a large glass bowl, combine the chopped shrimp with the diced onion, cucumber, and jalapeño.
Whisk together the lime juice, lemon juice, olive oil, sea salt, and black pepper in a small jar.
Pour the citrus dressing over the shrimp mixture and toss gently to coat every ingredient.
Fold in the diced avocado and chopped cilantro carefully to keep the avocado chunks intact.
Refrigerate for 15 to 20 minutes to allow the flavors to meld before serving chilled.