Remove the bluefin tuna from refrigeration 10–15 minutes before slicing so it loses extreme chill but remains firm. Pat dry with paper towels to remove surface moisture.

Trim and slice

Using a very sharp sashimi knife or long slicing knife, trim away any sinew. Hold the knife at a slight angle and cut the loin into 1/8–1/4 inch (3–6 mm) thick sashimi slices. Aim for even, clean strokes — typically 12–16 slices from 0.5 lb depending on slice thickness.

Prepare yuzu-kosho dressing

In a small bowl combine yuzu kosho and extra virgin olive oil. Add half the chopped dill, the lemon zest and 2–3 drops of lemon juice, and whisk until smooth. Taste and adjust: if the yuzu-kosho is very spicy, use a touch more olive oil; if too mild, add up to 1/2 tsp more yuzu kosho. Season lightly with 1/4 tsp sea salt flakes and a pinch of black pepper.

Dress the slices

Arrange sashimi slices on a chilled plate in a single layer or slightly overlapping. Using a spoon, lightly drizzle about 1/2 tablespoon of the yuzu-kosho/olive oil mixture across the slices, ensuring each piece gets a hint of paste but not overwhelmed. Reserve remaining dressing for finishing.

Finish with dill and seasoning

Sprinkle the remaining chopped dill over the dressed slices, then scatter the remaining 1/4 tsp sea salt flakes and the remaining pinch of black pepper evenly. Lightly zest a few more flecks of lemon over the fish for brightness.

Garnish & Serve

Plate the sashimi with microgreens or baby dill and the thinly sliced cucumber or daikon alongside or beneath the fish for texture contrast. Sprinkle toasted sesame seeds sparingly over the fish for visual contrast and a subtle nutty note.

Serve immediately with small dishes of chilled soy sauce on the side. Advise diners to use soy sparingly so as not to overpower the yuzu-kosho and olive oil flavors.

If desired, drizzle any remaining yuzu-kosho dressing in a fine stream over the plate tableside for aroma and presentation.