In a food processor or blender combine cut up cucumbers, tomatoes, garlic, green onions, parsley, and vinegar; cover and process until nearly smooth. (If using blender, blend half of the vegetables at a time.) Transfer puree to a bowl; stir in chicken broth.
Serve immediately or cover and chill up to 4 hours. Before serving, add sour cream and whisk until smooth. Stir in salt and pepper. If desired, garnish with slices of cucumber and wedges of tomatoes. Makes 6 side-dish servings.