For Aguachile: 1/2 cup packed cilantro leaves 3 cloves garlic, sliced 1/2 serrano chile pepper, sliced, or to taste 1/3 cup fresh lime juice, from 2 to 3 limes 1/3 cup water 1/2 teaspoon kosher salt 1/4 teaspoon ground black pepper 1/4 teaspoon white sugar For Shrimp: 1/2 pound raw shrimp - peeled, meticulously deveined, and sliced in half horizontally if large 1/3 cup thinly sliced red onion 1 cu…