Prepare the shrimp: Ensure the shrimp are fully peeled, deveined, and cut into bite-sized (about 1/2 inch) uniform pieces. Place the cut shrimp into a non-reactive glass or ceramic bowl.

Cure the shrimp: Pour the fresh lime juice over the shrimp, ensuring they are completely submerged. Add 1/2 teaspoon of salt. Stir gently, cover the bowl, and refrigerate for 15 to 25 minutes. The shrimp will turn opaque pink when fully cured.

Prepare vegetables while shrimp cures: Finely dice the red onion, tomatoes (removing seeds prevents excess liquid), and mince the jalapeño. Chop the cilantro.

Combine ingredients: Once the shrimp is opaque, drain off about half of the excess lime juice. Add the diced red onion, tomatoes, jalapeño, remaining salt, and black pepper to the bowl. Stir gently to combine.

Marinate briefly: Stir in most of the chopped cilantro (reserve some for garnish). Allow the mixture to sit in the refrigerator for another 5 minutes to let the flavors meld.

Serve: Just before serving, gently fold in the diced avocado. Taste and adjust salt or lime if necessary. Serve immediately with tortilla chips, tostadas, or saltine crackers.