Great party fare. These can be made ahead (roll tuna and chill overnight, covered; resume with cooking steps the following day). from Floridatable.com, this recipe is from Chef David Swhwadron, a Miami caterer.
Combine black and white sesame seeds in bowl. Dredge tuna in seed mix, rolling gently to cover completely.
Heat olive and sesame oils in large nonstick pan over medium high heat. Reduce heat to medium and place tuna in pan, searing until white seeds are lightly browned, about 2 minutes. Turn carefully so seeds don't fall off. Cook 2 minutes more. Remove from heat and let rest a few minutes.
Place tuna on bottom halves of rolls. Top each one with sweet wasabi ketchup. Cover with toll tops and serve.