
Make the ponzu. Whisk soy sauce, lemon juice, lime or yuzu juice, mirin and rice vinegar. Chill until needed.
Curl the spring onions. Slice spring onions lengthwise into fine strips. Soak in ice water for 10 minutes to curl, then drain.
Chill the tuna. Freeze the tuna for 10 minutes to firm it up for easier slicing.
Slice. Trim any bloodline, then cut against the grain into 1 cm slices, using one long stroke per slice.
Arrange. Lay the slices in a ring in a shallow bowl. Top each with a jalapeño slice.
Dress and serve. Pour the ponzu around the tuna. Dot with chilli oil and sesame oil, top with spring onion curls and serve immediately.