Lightly brown beef and onions together in a skillet. Using a 4-quart baking dish, combine the vegetables, soup, water,rice,pepper,bean sprouts, water chestnuts,and soy sauce.. Stir in prepared meat mixture. Cover the dish and bake at 350^ for 1 hour and 15 minutes, stirring occasionally, adding water if necessary. Uncover and sprinkle with the noodles. Return to oven and bake uncovered for another 10 minutes.