For stuffed portobellos, heat the oven to 180 degrees. Clean the portobellos well, cut off the stems and save them. Scoop out the mushrooms with a small spoon.
Fry the heads in oil and place them in a buttered baking dish. Finely chop the stems and fry them with the young onion rolls as well.
Then mix well with the remaining ingredients of the filling and season to taste. If the mixture is too liquid, bind it with breadcrumbs.
Fill the heads and sprinkle with the grated mozzarella.
Bake stuffed portobellos in the oven at 180 degrees for about 10-15 minutes. The mushrooms should be soft and the cheese melted.