Preheat the grill to medium heat. Lightly oil grate.
Mix the avocado, mango, lime juice, ground ginger, and wasabi powder in a bowl.
Season to taste with salt and pepper. Set aside until ready to serve.
On a shallow dish, spread the sesame seeds over the bottom.
Brush the tuna steaks with the oil, Then dip them into the sesame seeds on both sides.
Place tuna steaks on the grate of Preheated grill. Cook until fish turns opaque, turning once (Time is related to thickness, about 4 minutes for 1 inch thick steaks).
Serve immediately with summer salsa and additional wasabi on the side.