Arrange shrimp in an even layer onto a large platter or two smaller plates. Evenly coat shrimp with lime juice and a sprinkle of salt. Cover and refrigerate for 20 minutes.
In a blender, add serrano peppers, garlic, cilantro, fish sauce, lime juice, and salt and blend until smooth.
In a small bowl, sprinkle a pinch of salt onto the red onions, soak in water, then add a splash of white vinegar. Set aside.
After 20 minutes in the fridge, pour the sauce all over the shrimp. Make sure each piece of shrimp is well coated in the sauce. This can be kept in the fridge for up to 4 hours before serving.
To serve, drain the red onions and the radishes. Garnish with diced cucumbers, red onions, radish, avocado, and cilantro.
Serve immediately with your favorite tortilla chips.