In cities with plentiful sun and water somehow growing crops (greens, herbs, smaller annual foods) on buildings. Would this be on the walls or the roofs? I don't know, but it would have benefits if it could be done practicably.
More vegetation in a city would alleviate a portion of CO2, it could aid in insulating the building from sunlight, etc. Specialty crops could be grown locally and save outlying farmland for other, big crop items.
The technology included would be in how it is facilitated and potentially monitor and irrigation systems.