Place veal, onion, salt, pepper and water in Dutch oven. Bring to a boil. Reduce heat to low; simmer, covered, until meat is tender (about 30 minutes).
Preheat oven to 350 degrees F. Mix cooked spaghetti, undrained mushrooms and sour cream into veal mixture. Turn into greased 2 1/2 qrt casserole.
For Topping, melt shortening in small skillet; stir in bread crumbs. Remove from heat; stir in cheese and parsley. Sprinkle over veal mixture.
Bake, uncovered, for 35 to 40 minutes or until mixture is bubbly and crumb topping is golden brown.