This is a really deliciously fresh dish. It can be used for canapes as well. Some things to remember is to make this 1/2 hour before you want to serve it. All the chopping can be done in advance and then mixed last minute. If you assemble it too early the seasoning will take over and you will loose the fresh tuna flavor. The lime and salt in the soya will begin to cook the tuna and change its texture.
When adding the lime be careful not to add too much. You want to know its there but too much will take over the dish.
You can extend the dish by adding a bowl of rice, or serve the tartar on a bed of rice.