How to Make It
In a large bowl, lightly mix the chopped tuna with the chives and olive oil and season with 1/2 teaspoon of salt and a large pinch of pepper. Shape the mixture into 4 burgers, then cover and refrigerate.
In a small skillet, toast the sesame seeds over moderate heat, shaking the pan, until golden, about 3 minutes. Transfer the seeds to a place to cool. In a large bowl, toss the shredded cabbage with the carrots, sesame seeds, vinegar and sesame oil. Season with salt and pepper, cover and refrigerate for up to 4 hours.
Light a grill. When the fire is very hot, grill the burgers, turning once, until nicely charred and still very rare, about 1 minute per side. Grill the buns, cut side down, until toasted.
In a large skillet, combine the soy sauce, mustard and wasabi and bring to a boil over moderately high heat. Add the duna burgers and cook, turning once, until glazed with sauce but still rare, about 1 minute. Set the burgers on the buns. Fold the nori into the slaw and serve alongside.