Cut the mackerel into fillets and cut into small pieces. Grease the baking dish with vegetable oil and put the onion cut into thin half rings on the bottom. Put the fish on top. Sprinkle with lemon juice, salt and pepper. Finely chop the green onions and put them on the fish, season with soy sauce on top.
Cut the tomatoes into thin slices and put them on the green onions. Put the fish in the oven at 190 g for 15 minutes.
Then pull out the form with the fish and put the grated cheese on top. Put the mold in the oven again for 7-10 minutes.