Wash the mushrooms well and separate the stems and caps.
Lightly fry the finely cut onion in a frying pan with plenty of extra-virgin olive oil. Add the sliced carrot and cook for a few more minutes.
Add the finely chopped mushroom stems and cook for ten more minutes. Add salt and pepper.
Add the meat and break it up while cooking over a medium heat. When it starts to brown, add the tomato sauce.
Preheat the oven to 180 ºC. Arrange the mushroom caps facing upwards on a baking tray and drizzle or brush with a little extra-virgin olive oil.
Use a teaspoon to stuff the mushrooms with the meat filling.
Sprinkle some grated Parmesan cheese over each mushroom and bake for 25 minutes at 180 ºC.