In a small bowl, combine the sesame seeds, garlic powder, kosher salt, and pepper.
With paper towels, pat ahi dry, and coat all sides with soy sauce. Sprinkle with sesame mix, and press to adhere.
Heat your pan on high. Once it's super hot, add the oil, and allow it to start smoking slightly. You can test that your pan is ready by adding a drop of water to your pan, it should sizzle.
Grab tongs and a splash guard, add your ahi, and press it down with the back of a spatula to ensure the entire surface sears (ahi tends to curl at high heat). Place the splash guard on top, and continue to sear until it lifts easily and is golden, should be between 45 seconds - 1 minute. Repeat on the second side.
Use tongs to hold the ahi upright, and sear along the edges as well, rotating to get all the edges.
Place on a cutting board and allow your ahi to cool for 10 minutes before slicing. Enjoy!