Cover onions with very cold water in a small bowl and let soak for 10 minutes. Drain the onions and place them in a salad bowl, along with lettuce, tomatoes, potatoes, basil, capers, olives and cheese.
Whisk together tomato juice, oil and vinegar in a small bowl. Season with salt and pepper. Pour over the salad and toss.
Note: Ricotta salata, a firm, salted ricotta, can be found at well-stocked cheese shops and Italian markets.
1/2 starch, 1 vegetable, 1 fat