Place pork chops in bottom of 9" x 13" baking pan. Cut onion into thin slices and arrange in the pan all over the chops. Add mushrooms (if desired) and salt & pepper to taste. In small mixing bowl, add the mushroom soup and use the cup of water to rinse out the soup can and add this to the soup in the bowl. Wisk or stir the soup and water mixture for a few seconds until combined. Pour this over the chops and onions. Bake at 400 degrees for approximately 50 minutes until chops are no longer pink and top is lightly browned. Serve with the onion (and mushrooms), but not with the extra gravy unless you can spare a few extra carbs.