This soup just screams "summer" with its bright, refreshing flavor and cool temperature. Holding out a little bit of the bell pepper and tomato for a fresh relish garnish adds textural variety—some crunch and chew to contrast the smooth soup. A high-powered blender will yield the silkiest results, but a regular blender works well, too (just be sure to blend for several minutes). You can make the soup a day ahead and keep it chilled; just give it a good whisk or another turn in the blender before serving.
How to Make It
Dice bell peppers to equal 1/4 cup; reserve. Dice tomatoes to equal 1/4 cup; reserve. Roughly chop remaining bell peppers and tomatoes, and place in a blender. Add cucumber, garlic, vinegar, salt, 3 tablespoons oil, and 1 tablespoon lemon juice to blender; process on high until very smooth, 1 to 2 minutes. Chill 1 hour.
Stir together reserved 1/4 cup bell peppers and 1/4 cup tomatoes in a small bowl. Add onion slices and remaining 1 1/2 teaspoons lemon juice, and toss. Ladle chilled soup evenly into each of 6 bowls. Top each serving with pepper-tomato mixture, and drizzle evenly with remaining 2 tablespoons oil.