1. Place tomato, avocados, onion, green bell pepper, and lemon juice into the bowl of a food processor, and process until smooth. Pour in 1 cup tomato juice, and process to blend.
2. Transfer mixture to a large bowl, and mix in remaining tomato juice and 1 cup yogurt. Season to taste with salt. Chill for 2 hours.
3. Serve in bowls garnished with dollops of yogurt, chives, and a sprinkling of cayenne pepper.