Rinse the mushrooms well and pat dry. Remove the stems by carefully twisting them free by hand or by scooping them out with a small spoon. Chop the stems and set them aside.
Preheat the oven to 450 degrees F.
In a large skillet, saute the onions and garlic in the oil on medium heat for about 8 minutes, until golden. Stir in the chopped mushroom stems and continue to saute for another 2 minutes. Add the basil, parsley, bread crumbs, and salt and pepper. Cook for another 2 or 3 minutes, stirring constantly, and set aside.
In a mixing bowl, combine the sherry and soy sauce. Tumble the mushroom caps in the sauce to thoroughly coat them. Fill each mushroom with the sauteed bread crumb mixture.
Arrange the stuffed mushrooms in a nonstick or very lightly oiled or sprayed baking pan and bake, uncovered, for 15 to 20 minutes, until the mushrooms begin to release their juices and the filling is browned and crunchy. Serve hot.