Put some water in a pot then bring to a boil. Meantime, fill up a medium bowl with ice water and set aside.
Add shrimp to boiling water and let it cook. Your shrimp should be pink, opaque and cooked through (about 2 to 3 minutes). Use a colander to drain the shrimp then carefully place in the ice water bowl and let it cool for a bit. (If you don’t want to use ice water, just set it aside and let it cool for about 10 minutes, so you could easily handle it)
Drain shrimp really well then chop into ½ inch pieces and transfer to a bowl.
Add lime juice, lemon juice, onion, tomatoes, cilantro, jalapeno pepper to the shrimp bowl. Sprinkle some salt and pepper according to taste, then mix to combine everything.
Place in your fridge and let it sit for 30 minutes to 1 hour.
Add in the cucumber and avocado before serving (if you want you can strain off a little bit of the extra juices)
Enjoy this delicious ceviche with crackers or tortilla chips!