Cook vegetables according to label directions: drain.
Saute onion, green pepper and celery in margarine until tender.
In jar, combine 1/2 cup of the milk with the flour, salt and pepper: shake until smooth.
Add to onion mixture with remaining milk.
Cook over medium heat: stir until thickened.
Add cooked vegetables, Parmesan cheese and beef. Turn into deep 2-quart oblong baking dish.
Prepare pastry for single crust.
Blend cheese into pastry dough.
On lightly floured board roll dough to fit casserole.
Make small slits in dough and place over meat mixture.
Bake in hot oven, 400 degrees, 30 minutes or until crust is browned.