1. Preheat oven to 350°.
2. Combine egg whites, 1/4 teaspoon salt, and pepper in a large bowl, stirring with a whisk. Add beef, bell pepper, onion, and 1/2 cup tomato sauce to egg mixture. Place bread pieces in a food processor; process until fine crumbs form. Add crumbs to beef mixture, mixing with hands just until combined. Shape beef mixture into an 8 x 5–inch loaf. Place on a foil-lined baking sheet coated with cooking spray.
3. Combine remaining tomato sauce, remaining 1/4 teaspoon salt, sugar, vinegar, and Worcestershire sauce in a small bowl, stirring with a spoon. Reserve 2 tablespoons tomato sauce mixture. Spoon remaining sauce mixture over top of loaf.
4. Bake at 350° for 45 minutes or until done. Remove from oven, and spoon reserved sauce over meat loaf. Let stand 10 minutes before cutting into 8 slices.