Place the fish fillets into a 20x30cm glass baking dish. Slice the lemons in half and squeeze the juice out over the fillets, turning them to coat thoroughly. Sprinkle steak seasoning to taste over both sides of the fillets.
Lay a slices of Swiss cheese over the fillets so they are covered. Place tomato slices over the cheese. Sprinkle dried oregano over the top.
Bake for 20 minutes in the preheated oven, or until fish flakes easily with a fork.