In a medium bowl, combine the fresh lime juice, lemon juice and cold fish stock or clam juice (if using). The stock mellows and deepens the marinade; if you prefer purely citrus, omit the stock and use additional lime juice (increase by 2 tbs).

Flavoring

Add the grated ginger, grated garlic, chopped cilantro stems, aji amarillo paste, and minced aji limo or serrano (if using). Stir to combine thoroughly.

Season and blend

Whisk in 1 tsp sea salt and 1/4 tsp black pepper. Taste and adjust acidity and salt — the leche de tigre should be bright, slightly salty, and balanced with a hint of heat. If you want a silky emulsion, briefly blitz the mixture in a blender or use an immersion blender for 10–15 seconds, then chill for 5–10 minutes.

Fish and plating

Prepare fish

Check the fish for bones and pat dry with paper towels. Using a very sharp knife, slice the fish crosswise into thin, even slices about 1/8 to 1/4 inch (3–6 mm) thick. Arrange the slices in a single layer on a chilled serving plate or spread them slightly overlapping.

Dress with leche de tigre

Using a spoon, drizzle or gently pour enough chilled leche de tigre to lightly coat and almost submerge the fish slices — about 3/4 to 1/2 cup total depending on plate size. Allow the fish to 'cook' in the citrus for 1–3 minutes; tiradito is usually served shortly after marination so the flesh stays delicate and slightly firm.

Add garnishes

Scatter the thinly sliced red onion and microgreens or baby arugula over the fish. Drizzle 1 tsp chili oil and 1 tsp extra virgin olive oil in small drops across the plate. Sprinkle the fresh cilantro leaves and thinly sliced cucumber or toasted cancha (if using). Finish with a light pinch of sea salt to taste and a tiny grind of black pepper.

Serve

Serve immediately while the fish is chilled and the leche de tigre is bright. Provide small forks or spoons so diners can take fish with some of the marinade. Store any leftover leche de tigre separately in the refrigerator for up to 24 hours; do not store fish once marinated for more than a short time.