The fish is deliberately cooked a day ahead — escabeche is meant to sit in its vinegar-onion marinade overnight, and Margarita's vendors consider a fresh batch actually worse than one that's rested.
Fried king mackerel or other firm fish is layered with pickled onion, sweet pepper, and a vinegar-annatto marinade and left to cure until the flavors soak through. Food stands at Margarita's festivals and markets sell it cold, often with casabe or arepa.