1 Rinse tuna, pat dry and place in a bowl.
2 Rinse and dry scallions and cut diagonally into thin slices.
3 Peel ginger root and finely grate. Mix with teriyaki sauce, balsamic vinegar and scallions and pour over the tuna.
4 Cover tuna and let marinate for 2 hours in the refrigerator.
5 Lift tuna from marinade, pat dry and season with salt and pepper.
6 Heat the oil in a non-stick pan and cook tuna just until seared on the outside, about 2 minutes per side.
7 Put sesame seeds on a plate. Remove tuna from pan, sprinkle both sides with a little marinade and press into the sesame seeds.
8 Return tuna to pan and cook until crust is golden brown, 1-2 minutes on each side. Serve with the remaining marinade.