Cut the aubergine into square pieces around 3cm long and 3mm thick.
Heat a frying pan over a medium heat then brush the aubergine pieces with the sesame oil and cook them in the frying pan. Cook them for two to three minutes on each side, ensuring they are browned but not burnt. When cooked, place them on a tray.
Next, mix the mirin, miso and saké in a pan and heat over a low heat. Let it reduce then cover the aubergine pieces with this sauce.
Separate the tuna into chunks of around 3cm.
Plate the aubergine pieces, pour over the miso sauce and then position the tuna chunks on top. Sprinkle the chopped chives on top to garnish, then serve.