Crust and cube the bread and place in a medium bowl. Pour water over and let it soak for 10-15 minutes.

Chop the red onion, garlic, shallot, bell pepper, salt, cucumber, and 2 Tbsp of olive oil and stir to combine in a medium bowl. Let sit for about 15-20 minutes to allow the flavors to marry.

Squeeze the water out of the bread and add the bread to the vegetable mixture. Stir to combine.

In a large blender or food processor, add the bread-vegetable mixture in parts. While blending, add the avocado, sherry vinegar, and the last 2 Tbsp of olive oil. Add salt and additional vinegar as needed. Blend until smooth.

Refrigerate for 2-3 hours before serving. Serve chilled.