Start by cutting the pre-baked baguette in half
then spread some tomato sauce on top of each half of the bread
cut the mozzarella slices in half and place over the tomato sauce
lay the drained tuna and the onion strips, then cover with grated mozzarella cheese
place some sliced green olives and finally sprinkle some oregano on top
line a baking tray with aluminum foil and bake in a preheated oven at 200c (392f) until golden brown
and the appetizer is now ready to serve!