1Heat oven to 350ºF. Lightly grease cookie sheet. Unroll pizza crust on cookie sheet; gently stretch to form 12-inch circle.
2Layer beef, onions, mushrooms and cheeses on half of crust to within 1 inch of edge. Fold crust over filling; fold edge up and seal with fork. Cut slits in top.
3Bake 20 to 25 minutes or until crust is golden brown and filling is hot. Cool 5 minutes before cutting into wedges. Serve with mustard.