This is very quick and easy to make using basic ingredients but has bags of flavour. I have been making variations of this for years depending on what ingredients I have available. Suggested ingredient options: spring onions chopped finely and added at the end with the tuna; tinned sweetcorn; a splash of Thai fish sauce adds a nice Thai style flavour; a large carrot sliced thinly and softened with the onions. You can experiment yourself to find your favourite version.
When the cupboards are empty this is a good recipe to tweak yourself by using whatever ingredients you have available.