In a mixing bowl, combine chicken, bread crumbs, 1/4 cup tomato soup, onions, egg white, and black pepper. Shape firmly into 2 loaves. In a skillet, heat oil over medium heat. Add loaves. Brown on both sides. Cook, covered on low heat for 25 minutes. Stir in remaining tomato soup, water, and mustard. Top loaves with cheese slices. Cook, uncovered for 10 minutes.