Preheat the oven to 350 degrees F (175 degrees C).
Place the fish fillets into a 9x13 inch 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.