Rinse and drain black beans and add to a food processor fitted with an S-blade.
Add garlic and squeeze juice from wedge of lemon into the beans.
Place lid on processor and turn on highest speed.
Slowly pour water into the chute while processor is running – adding just enough to create a smooth consistency. (You may not need to use all of the water.)
Add onion to processor and pulse until the onion is chopped and mixed through the spread.
Rinse cilantro and pat dry. Strip leaves from the stems and add to food processor. Discard stems.
Pulse processor until cilantro is chopped and mixed through spread.
Scrape spread into a serving bowl or storage container.
Serve immediately or store in sealed container in the refrigerator for up to 4 or 5 days.