Dump the contents of the tuna can, water and all, into a saucepan or frying pan on medium heat. Stir the tuna around, breaking it up as best you can, until it's flaky. Add the ginger, sugar, pineapple juice. and soy sauce and keep stirring until the moisture is mostly gone. But don't let it get too dry-- it should still be a bit moist and clumpy.

Taste and add more sugar or soy sauce if you think it needs it.

Let cool. Store in an airtight container in the fridge 3-4 days or freeze for up to 1 month.