Core and quarter tomatoes (no need to peel them). Remove seeds from bell pepper and rough chop along with cucumber and red onion. Peel garlic cloves.
Remove crusts from bread and tear into small pieces. Soak briefly in water, then squeeze gently to remove excess moisture.
In a high-powered blender, combine tomatoes, cucumber, bell pepper, red onion, garlic, and the soaked bread. Blend on high speed for 30-60 seconds until relatively smooth but still retaining some texture.
With the blender running on medium speed, slowly drizzle in the olive oil to create an emulsion. Add the sherry vinegar, salt, pepper, and cumin. Pulse several more times until just incorporated.
For an ultra-smooth gazpacho, pass the mixture through a fine-mesh sieve (optional).
Transfer gazpacho to a covered container and refrigerate for at least 2 hours, ideally overnight.
Serve in chilled bowls with your choice of garnishes.