Recipe from Chef Jeff Martinez, El Chile Cafe y Cantina, Austin

Gulf Coast fish (sushi grade)
lime juice
serrano peppers

Quantities depend on your preference. Marinate fish in lime juice for 3 to 8 hours, depending on the type of fish you purchase. Mix in cilantro, tomato, avocado, and serrano peppers when ready to serve. Serve on a hearty tostada rather than a thin tortilla chip.