In a blender, whirl tomatoes, cucumber, pepper, olive oil, salt, and vinegar until smooth. (You may need to blend in batches.) Season with additional salt and pepper to taste. Garnish with red onion, if desired.
Note: Nutritional analysis is per 1/2-cup serving.
Tomatoes with wine: Parcel 104's Master Sommelier, Randall Bertao, likes wines with clean, focused flavors and a medium acidity to balance the tomatoes--such as Charles Melton Rosé 2004 (Barossa Valley, Australia; $12) and Merry Edwards Sauvignon Blanc 2005 (Russian River Valley, CA; $27).