Spread third of potato slices in single layer, slightly overlapping, in bottom of prepared baking dish. Sprinkle with 1/4 teaspoon salt. Layer with half of sliced tomato. Top with half the onion, then half the shredded cheese. Continue layering with another third of potato, remaining tomato, onion and cheese, sprinkling potato layer with another 1/4 teaspoon salt. Top mixture with final layer of potato.