Preheat oven to 425°F. Following package directions, place pie crust circle in a 10-inch tart pan or 9-inch pie plate; trim or flute edge. Bake until just golden, 5 to 7 minutes; cool slightly; set aside. In a large skillet over medium heat, cook bacon until crisp, about 5 minutes.

Remove to paper towels; crumble; set aside. Pour off bacon drippings from pan. Add mushrooms and onion; cook, stirring frequently, until mushroom liquid evaporates, 6 to 8 minutes; cool. In a large bowl beat until smooth sour cream, eggs, salt, oregano and black pepper.

Pour over baked crust; top with cooled mushroom mixture; sprinkle with bacon. Bake for 15 minutes. Reduce heat to 300°F; bake until a knife inserted in the center comes out clean, 5 to 7 minutes longer.