If using raw shrimp, blanch them in boiling water for 2-3 minutes until pink and opaque, then immediately plunge into an ice bath to stop the cooking process.
Peel, devein, and chop the chilled shrimp into bite-sized pieces and place them in a large glass mixing bowl.
Finely dice the cucumber, roma tomato, and red onion, then add them to the bowl with the shrimp.
In a small jar or bowl, whisk together the lime juice, lemon juice, extra virgin olive oil, sea salt, black pepper, and garlic powder until emulsified.
Pour the citrus dressing over the shrimp and vegetable mixture, tossing gently to ensure everything is well coated.
Cover and refrigerate for at least 15-20 minutes to allow the flavors to meld and the shrimp to absorb the citrus.
Just before serving, dice the avocado and fold it gently into the ceviche along with the freshly chopped cilantro to maintain the creamy texture.