Lightly toast the sesame seeds in a pan on medium heat until lightly brown and fragrant; This can be done without any oil. Set the toasted seeds aside and spread them out on a dinner plate.
Brush the tuna steaks with olive oil and then dip into the sesame seeds, lightly coating each side. Season coated tuna with sea salt and cracked pepper.
Heat remaining olive oil (about 1.5 TBS) on full heat in a pan. Place both tuna steaks in the pan, and let sit for about 2 minutes, or until the side facing down is cooked to your liking. Flip the steaks onto the other side and cook for another minute or so, depending on how rare you like your tuna; I like mine medium-rare, so I don't sear it for very long.
Serve with a squeeze of fresh lemon juice and your favourite salad or some roast veg. That's it!