Step 1

In a 12-inch skillet, distribute the shrimp in an even layer. Add water to cover and sprinkle in 1 teaspoon salt. Set the pan over medium, cover and cook until the shrimp are light pink at the edges and beginning to curl, 6 to 9 minutes; occasionally rotate the skillet for even cooking.

Step 2

Off heat, use a slotted spoon to transfer the shrimp to a medium bowl; discard the poaching water. Stir the lime juice into the shrimp, then refrigerate, uncovered and stirring once or twice, until no longer warm, about 15 minutes, but no more than 30 minutes.

Step 3

Meanwhile, heat an 8- or 10-inch skillet, preferably cast-iron, over medium-high until water flicked onto the surface immediately sizzles and evaporates. Add the Fresno chilies, chipotle chili and garlic; cook, occasionally turning each item, until charred in spots, 7 to 10 minutes. If charring at different rates, transfer each item to a plate when done.

Step 4

When cool enough to handle, stem and seed the chilies. In a blender, combine the charred chilies and garlic, Worcestershire, Maggi, soy sauce and ¼ teaspoon salt. Blend until smooth, about 1 minute. Stir the puree into the shrimp mixture. Let stand at room temperature for 10 minutes, then taste and season with salt.

Step 5

In a wide, shallow serving bowl, evenly distribute the onion and cucumber. Using a slotted spoon, arrange the shrimp on top, then pour the sauce over them. Top with the avocado and tomato.