Unfold and stack 2 piecrusts; gently roll or press piecrusts together. Fit piecrusts into a 9-inch pieplate according to package directions; fold edges under, and crimp. Line pie shell with aluminum foil; fill with pie weights or dried beans.
Bake on lowest oven rack at 425° for 15 minutes. Remove weights and foil; cool.
Sauté mushrooms in hot oil over medium-high heat 5 minutes or until golden brown and liquid is absorbed. Set aside.
Combine cheeses; set aside.
Stir together eggs and next 3 ingredients in a bowl; add mushrooms, bell pepper, and olives.
Pour half of egg mixture into prepared crust. Sprinkle evenly with two-thirds cheese mixture. Top with remaining egg mixture; sprinkle with remaining cheese mixture.
Bake at 375° for 40 to 45 minutes or until set, shielding edges with aluminum foil to prevent excessive browning. Let stand 10 minutes before serving.