Preheat oven to 400 degrees F (200 degrees C). Grease a 15×10 inch roasting pan. Place the potatoes, green and red peppers, and onions in the pan and toss with the 2 tablespoons of vegetable oil. Bake in a preheated oven, uncovered, for 20 minutes.
Meanwhile, in a mixing bowl, combine egg, ground beef, parsley, Worcestershire sauce, garlic and bread crumbs. Mix thoroughly. Shape into a loaf about 8x4x4 inches.
When vegetables have cooked for 20 minutes, reduce heat to 350 degrees F (175 degrees C). Take roasting pan out of oven and stir in zucchini. Push the vegetables to the sides of the pan. Place the meat loaf in the center of the pan and pour the tomato sauce over the loaf and vegetables. Season with salt and pepper to taste.
Bake in a preheated oven, uncovered, for 30 minutes or until done.