This dish is all in the preparation. The escabeche will last in the fridge for future lunches or dinners, and is a great accompaniment to have handy. Then all you need on the day is a fresh piece of tuna and you are good to go.
Begin by combining the ponzu, soy sauce, mirin, sake and ginger in a medium-sized saucepan. Bring to a simmer over a medium heat to infuse, then remove from the heat and add the grapefruit and chilli. Allow to cool. Add the olive oil and store until needed. It will keep for a week in the fridge.
Lightly coat the tuna in olive oil and season liberally with salt and pepper. Heat a non-sti