On a flat plate, combine equal parts of white and black sesame seeds for a beautiful and crunchy coating. Roll the sushi-grade ahi tuna in the sesame mixture until fully coated.

Heat a non-stick pan over medium-high heat and drizzle a small amount of toasted sesame oil to coat the bottom. Once the oil shimmers, sear the coated ahi tuna for about 15-20 seconds on each side.

Remove the tuna from the pan and let it rest on a cutting board for 5 minutes. Slice into ¼-inch thick pieces.

In a small bowl, whisk together soy sauce, a pinch of chili flakes, rice vinegar, and freshly ground black pepper.

Arrange the sliced tuna on a serving platter and serve the dipping sauce on the side, garnished with thinly sliced scallions.