In a food processor bowl or blender container, combine half of the broth, yellow tomatoes, sweet pepper, banana peppers, garlic, and onion. Cover and process or blend mixture until smooth. Repeat with the rest of the same ingredients.
Transfer soup to bowl. Cover and chill for at least 4 hours or up to 24 hours. Transfer to an insulated bottle. Place diced plum tomato in a covered small container; pack in an insulated cooler with ice packs. If using chives, place in a self-sealing plastic bag; seal. To serve, pour soup into bowls or cups; sprinkle with chopped tomato and, if desired, chives. Makes 8 side-dish servings.