Separate crescent dough into eight triangles; place in an ungreased 9-in. pie plate with points toward the center. Press onto the bottom and up the sides to form a crust; seal perforations. Spread with mustard; set aside., In a large skillet, saute the asparagus, onion and mushrooms in butter until asparagus is crisp-tender. In a large bowl, combine the remaining ingredients; stir in asparagus mixture. Pour into crust. , Bake at 375° for 25-30 minutes or until a knife inserted in the center comes out clean. Let stand for 10 minutes before cutting., Freeze option: Cover and freeze unbaked quiche. To use, remove from freezer 30 minutes before baking (do not thaw). Preheat oven to 375°. Place quiche on a baking sheet; cover edge loosely with foil. Bake as directed, increasing time as necessary for a knife inserted in center to come out clean.