Preheat oven to 450°. let pie crust stand according to package directions; ease into a 9 inch tart pan with removable bottom. Line unpricked pastry with a double thickness of foil. Bake for eight minutes.
Remove foil. Bake for 4 -- 5 minutes more or until pastry is set and dry. Remove from oven. Reduce oven temperature to 375°. In a large skillet cook bacon until crisp. Remove bacon from skillet, reserving 1 tablespoon of the drippings in skillet; discard remaining drippings. Drain bacon on paper towels; crumble. Set aside.
For filling, cook mushrooms in the reserved bacon drippings until tender and liquid evaporates. In medium bowl combine mushrooms, crumbled bacon, cheese, and green onions. Spoon bacon mixture into crust. In a large bowl mix eggs and sour cream; stir until smooth. Spoon egg mixture over the bacon mixture.
Bake for 25 to 30 minutes or until light Brown and a knife inserted into center comes out clean. To serve immediately let quiche cool on wire rack for 10 minutes before serving. To store, place quiche on a wire rack; let cool for two hours. Place cooled quiche, uncut, in an airtight container. Chill up to 24 hours. Preheat oven to 350° place quiche on a baking sheet. Heat about 10 minutes or until warm in center. Cut into thin wedges.