Season the tuna liberally with salt, and let rest for 30 minutes. While the tuna is resting, prepare your sous vide container. Heat to 115 degrees Fahrenheit.
After 30 minutes, drizzle the tuna steaks with one tablespoon of sesame oil, and press the sesame seeds into the top and bottom of the steaks (you can cover the sides, too, if you’d like).
In a medium-hot pan, sear the tuna steaks for a minute on each side in another one tablespoon of sesame oil, or until the seeds are browned (but not burned).
Once the steaks are seared, transfer to a vacuum seal bag or zip-top bag, making sure all air is removed. Submerge and cook for 45 minutes.
Remove the steaks, and serve immediately or cool until ready to serve.