Prepare the Dipping Sauce: Whisk together the soy sauce, rice vinegar, grated ginger, honey, sesame oil, and sriracha in a small bowl. Set it aside to let the flavors meld while you prepare the tuna.

Pat the Tuna Completely Dry: Remove the tuna steaks from their packaging and pat them thoroughly dry with paper towels on all sides. This step is critical because moisture prevents a good sear.

Season the Tuna: Season each tuna steak generously with kosher salt and freshly ground black pepper on all sides.

Create the Sesame Crust: Mix the white and black sesame seeds together on a shallow plate. Press each tuna steak firmly into the seeds, coating all sides evenly and pressing gently to help them adhere.

Heat Your Pan Properly: Place your cast iron skillet over high heat and add the sesame oil. Wait until the oil shimmers and just begins to smoke, about 2 to 3 minutes.

Sear the First Side: Carefully place the tuna steaks in the hot pan, leaving space between each piece. Sear without moving for exactly 45 seconds to 1 minute, depending on thickness.

Sear the Remaining Sides: Use tongs to flip each steak and sear the second side for another 45 seconds to 1 minute. For thick steaks, briefly sear the edges by holding the tuna upright with tongs for about 15 seconds per edge.

Rest and Slice: Transfer the seared tuna to a cutting board and let it rest for 1 minute. Using a very sharp knife, slice against the grain into 1/4 inch thick pieces. Arrange the slices on a plate and serve immediately with the dipping sauce.