Heat a clean grill to high heat. Using an oil with a high smoke point, oil/season the grill to give is a slick surface.
Brush each side of the ahi tuna fillets with 1/2 TBSP of sesame oil. Sprinkle each side with salt, pepper, and sesame seeds. Gently press the sesame seeds down into the fillets to secure them a bit.
Place the fillets onto the grill and sear them for about 1.5 minutes. Carefully flip the fillets and let them grill for another 1-1.5 minutes.
When done, remove the fillets from the grill and let them rest for about 5-10 minutes.