Ingredients

• 1 pound sashimi-grade head-on shrimp or 12 medium shrimp, shells and heads removed and reserved for another use
• Sea salt
• 2 serrano chiles, stemmed and cut into 1/4-inch pieces
• 2 tablespoons water
• 4 tablespoons fresh juice from 4 limes
• Freshly ground black pepper
• 1/4 cup thinly sliced red onion
• 2 tablespoons diced seeded cucumber
• Tostadas and sliced avocado, for serving

Instructions

• Split shrimp in half lengthwise and discard any veins. Transfer to a plate, sprinkle all over with salt, cover with plastic, and refrigerate at least 1 hour and up to 2 hours.
• Meanwhile, in a mortar and pestle, combine chilies with a pinch of salt and pulverize thoroughly, then add water and continue to work until chilies are reduced to tiny bits. Alternatively, blend chilies with water in a blender or with an immersion blender until thoroughly blended. Add lime juice and season with salt and pepper.
• In a mixing bowl, toss shrimp with chili-lime marinade, onion, and cucumber. Season once more with salt and pepper and serve right away with tostadas and avocado.