Prepare the Shrimp:
Bring a large pot of salted water to a boil.
Add the shrimp and cook for 1-2 minutes, just until they turn pink and opaque. Immediately transfer the shrimp to an ice bath to stop the cooking process.
Once chilled, dice the shrimp into bite-sized pieces.
Marinate the Shrimp:
Place the shrimp in a mixing bowl. Pour the lime and lemon juices over the shrimp, ensuring they are fully submerged.
Cover the bowl and refrigerate for 20-30 minutes to allow the shrimp to soak up the citrus flavors.
Combine Ingredients:
Drain excess citrus juice, leaving a small amount for flavor.
Add the onion, tomato, cucumber, jalapeño (if using), and cilantro to the shrimp. Gently mix to combine.
Season with salt to taste.
Serve:
Spoon the shrimp ceviche into a serving bowl or individual cups. Garnish with diced avocado if desired.
Serve chilled with tortilla chips, tostadas, or crackers.