Soak the Baccala` for 12 hours in fresh water to remove the saltiness. Depending on the thickness of the baccala` you may have to soak it longer. Change the water every 3 hours.
In a deep oven pan, coated with olive oil, add the scallions cut to pieces, some potatoes cut in small cubes and a few pieces of tomatoes.
Add a layer of potatoes cut in wedges. Over the potatoes spread some scallions, tomatoes, olives and some grated cheese.
Spread the Baccala` over the potatoes. Add some more pieces of scallions, tomatoes and olives.
Fill the oven pan with water till 1/2 inch to the border of the pan.
Place the oven pan on the stove and cook the entire content for 30 min. at medium flame. Then place in the oven and cook for an additional 30 min. at 400F.