Place veal between 2 sheets of heavy-duty plastic wrap and flatten to 1/8-inch thickness, using a meat mallet or rolling pin. Cut into serving sized pieces; dredge pieces in flour.
Heat 1 teaspoon oil a large nonstick skillet over medium-high heat. Add half of veal, and cook 1 to 1 1/2 minutes on each side. Transfer veal to a serving platter; cover and keep warm. Repeat procedure with remaining oil and veal.
Add mushrooms and onions to pan, and sauté 1 1/2 minutes until tender. Combine beef broth, Marsala, and water. Add to pan, scraping pan to loosen browned bits. Remove from heat. Stir in tomato, salt, and pepper. Pour mushroom sauce over veal. Sprinkle with parsley, and serve immediately.