Step 1

In a blender, combine the cucumber, serrano pepper (with or without seeds, depending how spicy you want it), red onion, cilantro, lime juice, and salt. Blend just until smooth (over-blending may dull the bright green color of the cilantro).

Step 2

Just before serving, toss the shrimp with salt.

Step 3

Arrange the sliced cucumber and shrimp on a plate.

Step 4

Pour the salsa verde over the shrimp. Garnish with onion, avocado, cilantro, and ground chiltepín peppers, if using.

Step 5

Serve with tostadas. Eat right away, or wait a few minutes if you prefer the shrimp to cure slightly in the lime juice.