Ceviche verde estilo Guerrero

Keep the fish or shrimp on a bed of ice throughout preparation. Cut into 2 cm dice, season with fine sea salt, and pour over the fresh lime juice. Turn once to coat. Cover and refrigerate for 15–25 minutes maximum. The cure is done when the exterior of the pieces is opaque and lightly firm but the interior retains a just-tender, translucent core — not uniformly white and tight.

While the fish cures, place the tomatillos, serrano chillies, cilantro, and salt in a blender. Process to a loose, vivid-green sauce without cooking — the sauce should smell sharply of raw tomatillo and fresh herb, with no trace of cooked or dulled aroma.

Drain the cured fish or shrimp, reserving a little of the lime cure if a sharper finish is desired. Fold the green tomatillo sauce through the fish together with the diced cucumber. Add the olive oil and taste for salt. The mixture should be bright and lightly sauced, not swimming in liquid.

Immediately before serving, fold in the diced avocado with a single, light movement. Spoon into chilled glass copas. The avocado should remain in distinct, creamy pieces — green throughout, with no browning at the edges.

Serve at once alongside tostadas. The copa glass should feel cold to the touch at the table.