1Preheat the oven to 350°F.
2Remove the stems of the mushrooms. Chop the stems and set aside.
3Arrange the caps in an oiled baking dish.
4In a frying pan, stir together the butter, chopped stems, onion, salt and pepper.
5Cook until the onions are clear and soft.
6Stir in the lentils, cheese, and bread crumbs. Remove from the heat.
7Stuff the caps with the lentil mixture.