Rinse the tuna and pat dry. Cut into smaller 1-2 inch portions if necessary to fit snugly into a saucepan.
Put in a small saucepan with the oil, place over low heat until bubbles start to come to the surface.
Let cook for about 10 minutes, without letting the oil simmer or bubble too much.
Turn off the heat and add the garlic and herbs and any other flavorings.
Pour the contents into a glass jar. Let cool to room temperature, cover, and let infuse over night before serving.
Store in the refrigerator for up to two weeks.