Heat a large saute pan over medium high heat. Whisk together the miso and vinegar and put the dukkah on a small plate. Smear the miso mixture over each of the tuna steaks and then press them into the dukkah so it covers the outside of the tuna steaks.
Add 1 tablespoon of the sesame oil to the pan and sear the tuna steaks for 1-2 minutes per side so it is golden on the outside but still raw in the middle. Remove from the pan.
Add the last tablespoon of the sesame oil to the pan and heat until almost smoking. Place the bok choy cut side down in the pan and sear until just charred, flip and cook for a minute or two longer until the ends are bright green and the base is slightly softened.
Remove to a plate. Slice the tuna and place across the plate. Garnish with the green onions, Japanese seven spice and a little extra drizzle of the sesame oil.