Steps
1. Peel and dice the cucumber, onion, potato, and tomato.
2. Boil the diced potato until tender, then let it cool.
3. In a bowl, mix the rice vinegar, soy sauce, sugar, salt, and pepper to make the dressing.
4. Combine all the diced vegetables in a large bowl.
5. Pour the dressing over the vegetables and toss to coat evenly.
6. Chill the salad in the refrigerator for at least 30 minutes before serving.