Heat oven to 450°F. Spray cookie sheet with cooking spray.
In 10-inch skillet, heat oil over medium-low heat. Cook mushrooms and spinach in oil 5 to 7 minutes or until mushrooms are tender and spinach is wilted.
Unroll pie crust on cookie sheet. Spread mushrooms and spinach evenly over crust, leaving about 1 inch around edge. Fold crust edge over in 2-inch sections. Continue around whole pie.
Bake 18 to 20 minutes or until crust is golden brown and crisp.