Finely chop the onion and sauté in olive oil, then add half of the finely chopped clove of garlic, sauté briefly, now add the mushrooms (if they are very large, roughly dice) and fry briefly and add the rest of the clove of garlic, top with the finely chopped parsley and enjoy.
2nd variant:
As described above (except for the parsley), deglaze the whole thing with white wine and stir in sweet cream or creme fraiche and for those who don`t like white wine there is the variant with red wine and finally top with finely chopped parsley.
Tastes delicious with rice or as an accompaniment to meat.