Preheat oven to 350degrees. Press mashed potatoes onto bottom and up sides of a greased 9-in. deep-dish pie plate. Brush with 1 tablespoon oil. Bake 30 minutes or until edges are golden brown., Meanwhile, in a large skillet, heat remaining oil over medium-high heat. Add mushrooms; cook and stir 3-4 minutes or until tender. Add garlic; cook 1 minute longer. Remove from heat. Stir in spinach, bacon and rosemary; spoon over crust. In a small bowl, whisk eggs, milk and pepper until blended; stir in cheese. Pour over mushroom mixture., Bake 25-30 minutes longer or until golden brown and a knife inserted in the center comes out clean. Let stand 10 minutes before cutting.