Combine the cucumber and tomatoes in a blender, reserving 1/4 cup of each for garnish. Add the bell pepper, onion, vinegar, 1 teaspoon each dill and parsley, 1 clove garlic and the sugar; puree until smooth. Pass through a fine mesh strainer into a bowl, pressing with the back of a spoon to extract as much liquid as possible. Season with 1 teaspoon salt. Refrigerate until chilled, about 1 hour.
Meanwhile, make the croutons: Heat the remaining clove garlic with the olive oil in a skillet over low heat. Add the bread cubes and the remaining 3 teaspoons each dill and parsley. Cook, stirring, until golden and crunchy, 10 to 15 minutes. Discard the garlic.
Pour the soup into chilled bowls. Dice the reserved cucumber and tomatoes; sprinkle into the soup. Garnish with the croutons.