Start by peeling and deveining the shrimp if not already done, then pat them dry with a paper towel.
In a bowl, combine shrimp with lime juice, sea salt, and black pepper. Let marinate in the refrigerator for 15-20 minutes.
While the shrimp marinates, dice the tomato, finely chop the red onion and cucumber, and mince the jalapeño. Roughly chop the cilantro.
Cut the avocado in half, remove the pit, and dice the flesh into cubes.
After marination, gently toss the shrimp with the chopped tomato, red onion, cucumber, jalapeño, and cilantro in a large bowl.
Carefully fold in the diced avocado to avoid mashing it, ensuring a good mix of all ingredients.
Taste and adjust seasonings if needed, then serve immediately for the freshest flavor.