To begin, place the cleaned and butterflied shrimp in a large bowl. Ensure that the shrimp are fresh and free of shells and veins. For best results, keep them chilled while preparing the remaining ingredients.

In a blender, combine the jalapeño or serrano peppers, lime juice, water, and a pinch of salt. Blend until smooth to create the chili-lime marinade. Taste and adjust for heat, add more peppers for spicier flavors or balance with extra lime juice if necessary.

Pour the chili and lime marinade over the shrimp, ensuring all the shrimp are fully submerged. Stir gently to coat. The acidity from the lime juice will "cook" the shrimp. Let the shrimp marinate in the refrigerator for 15-20 minutes, or until they turn opaque and pink.

While the shrimp are marinating, thinly slice the cucumber and red onion. Set them aside for later assembly. The thin slices allow the vegetables to absorb the marinade's flavour and add a refreshing crunch to the dish.

Once the shrimp have marinated and "cooked" in the lime juice, remove them from the refrigerator. Add the cucumber and red onion to the bowl, gently tossing everything together. This step incorporates the fresh, crisp vegetables into the dish.

Season the entire mixture with salt to taste. Be cautious not to over salt, taste as you go. The flavors should be balanced between the brightness of the lime, the heat of the chili, and the savoury shrimp.

For additional texture and flavour, add thin slices of avocado on top. The avocado provides a creamy contrast to the sharp and spicy notes of the dish. You can also garnish with freshly chopped cilantro for a burst of freshness.

Serve the aguachile immediately with tortilla chips or crispy tostadas on the side. Aguachile is best enjoyed chilled, making it a perfect dish for hot weather. You can also add extra lime wedges or chili for diners who enjoy more citrus or spice.