Cut out the cores of the onions, make continuous cuts on one side. Carefully remove the onion rings, chop the small rings for the filling.
Heat a frying pan with vegetable oil and fry the mushrooms for 3-4 minutes.
Prepare the filling. In a bowl, mix the minced meat, chopped onion, herbs, mushrooms, salt, pepper, and spices.
Grease a baking dish with oil. Fill the onion halfway with the stuffing, put a piece of mozzarella and fill the rest with the stuffing.
Place the onion bombs in a baking dish and cover with foil. Bake the onions in the oven for 20-30 minutes at 200°C. Then remove the foil, brush the bombs with vegetable oil, sprinkle with grated mozzarella and bake for another 10 minutes until golden brown.