Marinate pork chops in 1/4 cup Italian salad dressing for 3 hours, turning occasionally. Remove chops from marinade. Brown chops on both sides in oil in skillet over medium heat. Sprinkle with salt and pepper. Return browned chops to marinade in baking dish. Layer potatoes and onion over chops. Dot with margarine. Pour remaining 2 tablespoons of Italian dressing; sprinkle with Mozzarella cheese over top. Cover with foil. Bake at 375 F for 1 hour and 15 minutes or until chops and potatoes are tender.