1/4 cup kosher salt, plus more for seasoning
1 pound medium shrimp, peeled and deveined
2 lemons, juiced
2 limes, juiced
2 oranges, juiced
1 cup cucumber, peeled, seeded and diced into 1/4-inch pieces
1/2 cup red onion, finely chopped
2 Serrano chiles, seeded and finely chopped
1 cup seeded and diced tomatoes
1 Hass avocado, peeled, seeded, and chopped into 1/2-inch pieces
1 tablespoon roughly chopped cilantro leaves, plus leaves for garnish
1/4 cup extra-virgin olive oil