[jyl]

Not sure (what kind of tuna), maybe yellow. This works w/ other firm fishes too, swordtail and so on. You can also get the sweetness from brown sugar or mirin (may need a touch of cornstarch for quick thickening if mirin), and the heat from chili sauce or red pepper, it's all a bit different but good. For more crust, you can press sesame seeds into the tuna along with the pepper.