Preheat oven to 325 F. Remove the stems from the mushrooms and reserve them for another recipe. If you want you can mince some of the stems and include them with the stuffing mix. Combine the bread crumbs with the sour cream and mix until well blended. Add onion and green peppers. Mix well.
Fill each mushroom cap with the stuffing mix and place on a cookie sheet.
Bake for 20 - 30 minutes or until hot. Remove from oven. Garnish with sliced olives and serve as a great appetizer.
CAUTION: Since mushrooms contain a large amount of water it is necessary for these little beauties to cool a little before eating. The very hot water in them can cause burns to the mouth and then your guests can''t enjoy the entree.