Cut a shallow slice from each potato to form a flat bottom for each stack. Cut each potato lengthwise into 3 slices. Scrape brown gills from the underside of the mushrooms with a knife and discard. Slice mushrooms, zucchini, tomatoes and onion into 1/4-inch-thick slices. Assemble potato stacks in this order in microwave-safe dish: bottom potato slice, 2 zucchini slices (do not overlap), 3 to 4 onion slices, 3 to 4 mushroom slices, salt and pepper, 1 tablespoon cheese, 1 teaspoon Italian dressing, middle potato slice, 2 tomato slices, 2 zucchini slices, salt and pepper, 1 tablespoon cheese, 1 teaspoon Italian dressing, top potato slice. Secure each stack with 2 toothpicks. Drizzle with remaining Italian dressing. Cover tightly with plastic wrap. Microwave on high for 16 minutes (cooking time may vary depending on your microwave) or until potatoes are done. Use oven mitts or tongs to remove from microwave. Remove plastic wrap carefully to prevent burns from steam.
If requiring a gluten-free recipe, check the label of the indicated (*) recipe ingredients to ensure they are gluten-free.