If using raw shrimp, peel, devein, and lightly poach them until just cooked, then chill. If already cooked, ensure they are chilled.
In a bowl, combine the shrimp with lime juice, olive oil, salt, and pepper. Let the shrimp marinate in the citrus for about 10-15 minutes, allowing the flavors to meld.
Dice the avocado, tomato, red onion, and cucumber into small, bite-sized pieces. Finely chop the cilantro.
Gently toss the diced avocado, tomato, red onion, cucumber, and cilantro together.
Carefully fold the marinated shrimp into the vegetable and avocado mixture, ensuring an even distribution of flavors.
Taste and adjust the seasoning with additional salt, pepper, or lime juice if needed.
Serve immediately for the best texture, or chill for an extra refreshing ceviche.