Wash all vegetables thoroughly under cold running water. Core the tomatoes, remove the seeds from the bell pepper, peel the cucumber (leaving some strips of skin for color if desired), and peel the red onion. Rough chopping is sufficient as everything will be blended.
In a large food processor or blender, combine half the tomatoes, cucumber, bell pepper, red onion, and all of the garlic. Pulse until coarsely chopped but not completely pureed.
Take your day-old bread slice, remove the crusts, and soak it in cold water for about 1 minute. Then squeeze out excess moisture.
Add the soaked bread, olive oil, vinegar, salt, pepper, and cumin to the vegetable mixture. Blend until completely smooth, approximately 1-2 minutes.
Add the remaining tomatoes, cucumber, bell pepper, and red onion. Pulse briefly just to incorporate – about 3-5 pulses.
Taste your gazpacho and adjust the seasoning as needed. Remember that cold temperatures dull flavors, so season slightly more aggressively than you might for a hot soup.
Transfer the gazpacho to a large bowl or container with a tight-fitting lid. Refrigerate for at least 2 hours, though overnight is ideal if time allows.
Serve well-chilled in bowls or glasses, garnished with diced vegetables, a drizzle of olive oil, and fresh herbs.