In large skillet, brown sausage and onion, breaking up meat with back of spoon. Drain and spoon into 8-inch pie dish. Cover with cheese. Wrap in foil and place inside ziploc freezer bag. Label and freeze.
To serve: Defrost and bake at 350 degrees for 15-20 minutes or until cheese is melted. Serve with warm corn tortillas and sour cream and fresh salsa on the side.