Clean your raw shrimp cut in half and take out the black string then rinse

This is what I mean by black string

Squeeze lime juice enough to cover the shrimp I usually use the whole bag like 8 or more limes

Then cut Serrano peppers in halves and remove the seeds

Add chile to a half cup of lime juice and blend it

Cover shrimp in lime and pepper juice refrigerate

Slice red onion

Chop cilantro

Slice cucumber

Add your onion, cilantro and cucumber to your shrimp

Serve on tostadas with avocado slices