Bring a small pot of water to a boil, add the shrimp for 2 minutes until pink and opaque, then immediately plunge into an ice bath to stop the cooking.
Drain the chilled shrimp, pat dry, and chop into bite-sized pieces before placing them in a large glass mixing bowl.
Add the lime juice, chili powder, sea salt, and black pepper to the shrimp, stirring well to ensure every piece is coated.
Finely dice the cucumber, roma tomato, red onion, and jalapeño, then fold them into the shrimp mixture along with the chopped cilantro.
Cover the bowl and refrigerate for at least 20 minutes to allow the citrus to marinate the ingredients and develop the flavors.
Just before serving, dice the avocado and gently fold it into the ceviche to keep the pieces intact and creamy.
Serve chilled in a bowl or over a bed of greens for a clean, protein-packed meal.