In a frying pan, melt the butter over low heat.
Add all the ingredients, besides the fish.
When the sauce has simmered over medium heat for a few minutes, add the tuna steaks.
Fry them till slightly brown on both sides. You can turn the heat up quite a bit. Don't over cook it! Slightly pink in the middle is what you are going for, and tuna is great and healthy raw.
Serve with a fresh Greek salad, and poor some of the left over sauce creatively onto your plate for extra flavour.