1. Using a pestle and mortar, crush the toasted sesame seeds.
2. Season both sides of the Tuna with some salt.
3. Apply some wasabi paste on both sides of the Tuna.
4. In a platter lay the crushed sesame seeds, and press all the exposed surfaces of the Tuna onto it, to coat it completely. Set aside for 2 minutes.
5. In a frying skillet, heat the oil, on medium flame. When the oil begins to smoke, add the coated Tuna and turn the heat down to medium low.
6. Using a fish spatula, try to turn the fish to the other side, when it ceases to stick to the bottom of the pan. Cook the other side, as well as the other faces of the fish, in a similar manner.
7. Serve with a mayonnaise dip and fresh salad, as a complete meal!