Moringa olifera is a tree with magic powers. It grows very fast - 3-5m per year - even in poor soils and can easily be grown from seed or cuttings without much attention. The tree provides many benefits:
- The leaves can be eaten (think of them as a leafy vegetable) and provide as much protein as eggs, 3 times more iron than spinach, 4 times more vitamin A than carrots, 7 times more vitamin C than oranges, 3 times more calcium than milk and 7 times more potassium than bananas, 
- The fruit is also edible and highly nutritious
- The leaves also make an excellent feed for livestock
- The crushed seeds can be used to purify water 
- The oil is highly nutritious, can be used as a fuel and also has cosmetic uses
Growing instructions can be found here. Seeds are cheap and can be bought here. The first shoot will come up about a week after the seed is planted, and a year later you will have a tree several meters high.
http://www.winrock.org/fnrm/factnet/factpub/FACTSH/moringa.htm - Good info on how and where to grow it