Pat the two tuna steaks dry with paper towels. Spread the sesame seeds on a flat plate and press both sides of the fish firmly into them, creating an even crust. Halve the avocado, remove the pit and slice the flesh into uniform slices. Meanwhile, mix the soy sauce with the wasabi in a small bowl until smooth and spicy. Have the edamame ready.
Heat a skillet with a good non-stick surface on high heat until very hot. Place the sesame-crusted tuna steaks in the pan and sear them on both sides for exactly one minute. The sesame seeds should lightly toast and form a crispy layer, while the core of the fish remains beautifully rare.
Immediately remove the tuna steaks from the hot pan to prevent overcooking and place them on a cutting board. Let the fish rest for a minute and then slice the steaks with a sharp knife without pressing into neat slices about one centimeter thick.
Distribute the sliced tuna over the plates. Arrange the avocado slices and edamame neatly beside the fish. Finally, drizzle the wasabi-soy sauce over the dish and serve immediately.