Thinly slice the ahi tuna and arrange on a plate. I like to arrange the slices separately (instead of overlapping) for this dish. This is so that the sesame oil and soy sauce and be drizzled evenly on all the slices.
Add the sesame oil to a small pan over medium heat. Heat until the oil gets super fragrant and nutty. Just as the sesame oil begins to smoke (this takes 1-2 minutes), turn off heat, and quickly pour the hot sesame oil over the sashimi.
Then drizzle the soy sauce on top. Sprinkle on some roasted sesame seeds if using (using white and black sesame seeds give a nice contrast). Eat right away and enjoy ^_^