Peel the onion and cut it into rings. Dissolve starch in cold water.
Prepare the sauce: Pour soy sauce into a preheated frying pan and add sugar. Add dried garlic and ground ginger. Add vegetable oil and honey. Mix all the contents. Pour the starch into the pan and, as soon as the mass begins to thicken, immediately remove from the heat and place it on a plate.
Wash the mackerel, cut off the head and tail, remove all bones. Cut lengthwise into two parts and place the carcass in a baking dish. Top it with the prepared sauce and finely chopped onions. Place the mackerel in the oven preheated to 180° and bake for 30-35 minutes.
Serve the fish lightly crumbled with grated cheese, boiled potatoes and seasonal vegetables.