Crumble ground beef into a large skillet. Cook over medium-high heat 3 minutes. Add onion and continue to cook until meat and onion are both browned. Drain off excess fat.
Mix in soup, Worcestershire sauce, seasoned salt, and mushrooms. Pour mixture into pastry-lined pan. Cover with top crust. Seal edges and cut steam vents in top.
Bake in preheated oven for 30 minutes, until crust is golden brown. Place slices of cheese on top of pie. Serve pie while hot.
