Pour soy sauce into shallow container and place tuna into soy sauce for 10 minutes. Flip pieces over and allow to sit in soy sauce for another 10 minutes.
Pour both types of sesame seed into a small plate and coat tuna on all sides by pressing the tuna into the seeds.
Put olive oil into pan and heat until it reaches smoking point.
Sear tuna on all sides for five seconds. Seeds are very likely to pop from the heat.
Pull tuna from pan and allow to rest for 10 minutes.