Wash and pat dry the mushrooms, cut them in quarters. Cook the onion in melted butter with a drop of olive oil until soft, add the garlic and the mushrooms. Crumble the gorgonzola cheese and throw on top of the mushrooms. Cook until the mushrooms turn soft and the cheese starts sticking to the pan. Pour in the cream and the herbs, season with salt and pepper. Stir with a wooden spoon until the sauce thickens. Pour the mushrooms in the sauce in a cocotte. In a separate bowl mix together the bread crumbs, oats and hazelnuts. Stir in the melted butter and olive oil, season well and mix in fresh herbs. Coat the mushrooms with the obtained crumble mixture and bake until topping is golden brown and crusted. Serve with a bowl of mixed salad.