
Prepare the fish. Cut the fish into portions. Add salt and pepper. Grease the baking dish with vegetable oil. Cut the onion into large half rings. Place it on the bottom of the dish. Place the fish on a bed of onions.

Prepare the sauce. Whisk the milk with the egg and salt. Pour the mixture over the fish. Cut the tomato into rings. Place on top of the sauced fish. Grate the cheese on a coarse grater and sprinkle it over the tomatoes. Preheat the oven to 180 degrees. Bake for 50-60 minutes.