1Heat oven to 400. Lightly spray a 2-quart casserole dish w/ cooking spray. Heat oil in lg skillet over medium heat.
2Add sausage, crumbling as you cook, until browned. Add mushrooms and onions. Cook until tender. Stir in pizza sauce and pepperoni slices. Cook until bubbly. Remove pan from heat.
3Stir into pan, both cheeses. Spoon mix into casserole dish. Place the pie crust over mix, crimping edges. Cut several slits in top of crust and bake 30 mins. Cool 10 mins and cut into 6 slices of pie.