Keeping the tuna very cold, toss gently with the scallion, cucumber and a bit of sea salt and freshly ground black pepper. In another bowl whisk the soy sauce, rice wine vinegar, ginger, garlic and Ginger Oil until well blended. Add to the fish mixture and toss to dress well.

Cut the nori into 1 1/2-inch rounds and mound the tartare mixture by the teaspoonful onto the nori rounds. Sprinkle with sesame seeds and serve immediately. Alternatively it can be served on an ice cold plate lined with lettuce leaves and garnished with marinated seaweed and sesame seeds, as an appetizer.

Note: To make Ginger Oil, combine lots of ginger scraps and canola oil in a small saucepan. Heat oil slightly, about 3 to 5 minutes over medium heat, then remove from the heat. Let steep for a couple of hours or up to a day, and strain.