Bring 2 quarts salted water to a boil, add the shrimp and cook just until pink and opaque, 1 to 2 minutes. Drain and plunge into a bowl of ice-water to stop the cooking process. Drain again, blot dry and squeeze the lemon over the shrimp. Refrigerate until chilled through, at least 30 minutes.
While the shrimp chills, prepare the cocktail sauce by combining the chili sauce, cumin, coriander, black pepper, cilantro, Worcestershire, 1/2 tablespoon horseradish, lime juice and tequila in a mixing bowl. Taste for seasoning and adjust the horseradish and black pepper to taste. Transfer to a small serving dish.
To serve, line a platter with lettuce and place the cocktail sauce in the center. Arrange the shrimp around the edge and garnish with a sprig of cilantro.
Notes
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