Rip the bread into large pieces and put them into a bowl. Add water to cover, then pull out the bread quickly and squeeze out the excess water, leaving squishy soaked bread.
Place the bread in a food processor or blender, and add the pimentos, lemon juice, garlic, paprika, cayenne and salt. Process until well blended. Add the olive oil in a very thin steady stream, using the insert made for this purpose or just doing it by hand. As the oil gets incorporated the mixture should emulsify (thicken).
Scrape the mixture into a bowl.
Notes
One thing I love about my food processor, and also many blenders, is that the top has an insert that allows you to pour the oil into it, and the a tiny hole allows the oil to very slowly get added to the mixture in the bowl, so that it emulsifies. Anyone who has ever tried to follow a recipe that says “drizzle in the olive oil very slowly while whisking” knows that this is a great invention.