Step 1Break the bread into big chunks and soak it in water to cover until it is softened, about 15 minutes. Squeeze out the excess water and place the bread in a blender or food processor with the garlic. Blend until the bread and garlic are smooth, scraping down the sides as necessary.
Step 2Add the tomatoes (it may be necessary to process the tomatoes in 2 batches) and the pieces of pepper and cucumber, if using, and puree. Add the cumin and salt. With the blender on, add the olive oil in a slow stream. As the oil is incorporated, the gazpacho will turn from tomato-juice red to a paler, orange color. Blend in the vinegar and enough water to make the desired thickness.
Step 3Place the gazpacho into a tureen, bowl or pitcher and chill until serving time.
Step 4Place each of the garnishes--chopped peppers, onion, cucumber and croutons--in small bowls or on a relish dish and pass them when the gazpacho is served. This gazpacho also can be served, thinned with additional water, in tall glasses for sipping, without the garnishes.