1. Fill a large saucepan three-fourths full with water. Bring to a boil over high heat. Prepare a large bowl of ice water.
2. Cut a shallow “x” in the blossom end of each tomato. Carefully slip the tomatoes into the boiling water and let cook for 30 seconds. Using a slotted spoon, transfer to ice water to cool. Remove from water and peel immediately.
3. Cut tomatoes in half and remove the core and seeds. In a blender or food processor, puree three of the tomatoes until liquefied and transfer to a large bowl. Reserve the remaining tomatoes.
4. Puree onion and garlic, adding a tablespoon of the vinegar if needed for a smooth consistency. Add to the bowl with the tomato puree.
5. Add cucumbers with another tablespoon of vinegar to the blender and pulse until coarsely chopped. Add to pureed tomato mixture. Chop remaining tomatoes coarsely in the blender, then add to mixture as well. Whisk in olive oil and remaining quarter cup vinegar. Season with salt and pepper.
6. Cover and refrigerate until well chilled, about two hours. Ladle into chilled bowls and garnish with diced green pepper and minced red onion to serve.