Step 1 - In a large bowl, marinate the fish with lemon, garlic, salt and pepper. Cover and refrigerate for at least 1 hour.
Step 2 - Preheat the oven to medium temperature (180ºC).
Step 3 - In a baking dish place a layer of onion, on top of the marinated fish and cover with cheese slices, tomato slices, oregano and slices of sausage.
Step 4 - Bake for 25 to 30 minutes. After 20 minutes pour the wine over the fish and finish cooking.