Chop the onions, spearmint and parsley very finely. Put the mince and all the remaining ingredients in a bowl. Knead, cover with foil and leave it for 1 hour.
Chop the marinated mushrooms finely and the cheese into cubes. Prepare a plate of flour as well.
Take a little of the mince and put it in your palm. Press on it to flatten it, then arrange mushrooms and cheese on it.
Cover with the same amount of mince and close. Shape into a meatball and roll in flour. Arrange the ready-to-fry meatballs in a platter or plate.
Heat up the oil and fry the meatballs on both sides.