Venezuela has been moving towards more urban agriculture over the last couple of years. But, as the report from Al Jazeera below shows, results have been mixed. In comparison, the urban agriculture movement in Cuba has done very well. I think the difference is in buy in; in Cuba, the population was faced with a crisis when their agricultural inputs collapsed. The Cuban government responded by removing roadblocks and creating support structures for both urban and rural small agricultural projects. The Venezuelan experience seems to have been more top down.
In North America, the rise of the city chicken is an indication that there is a strong desire for urban agricultural projects, but municipal bylaws keep getting in the way. If our governments were to get out of the way and quit forbidding (which is, I think, more accurate than "allow") more agricultural use of urban land, I don't think we would need much in the way of assistance to get a proper urban agriculture movement off the ground. The agro-ecological principles of farmer-to-farmer peer counselling would take off by itself.