Bring a medium pot of water to a boil and poach the peeled shrimp for 2 to 3 minutes until they are pink and opaque.
Immediately transfer the shrimp to an ice bath to stop the cooking process, then drain and chop into bite-sized pieces.
In a large glass mixing bowl, whisk together the lime juice, lemon juice, sea salt, black pepper, and chili flakes to create the marinade.
Add the chopped shrimp to the bowl and toss well to coat, then place in the refrigerator to marinate for 10 minutes.
While the shrimp marinates, finely dice the cucumber, red onion, roma tomato, and jalapeño.
Remove the shrimp from the refrigerator and gently fold in the diced vegetables and chopped fresh cilantro.
Just before serving, dice the avocado and carefully fold it into the mixture to ensure the pieces remain intact and creamy.
Serve the ceviche chilled in a bowl or portioned into large butter lettuce cups for a clean, crisp presentation.