Chayote

The Chayote, also known as a Choko or Christophine, is an edible plant in the Cucurbitaceae family.

How to start
Buy a fruit from a market, and leave it on the counter until the sprout reaches 6 inches tall, then plant it outside

Sources of fruit for growing
Various, I haven't found any websites carrying them, but, I found sellers of them on Ebay at the time of writing this. And have heard of people finding them at their market.

History
Needs info here

Folklore
In Australia, it was believed that McDonald's apple pies are made from Chayote, as opposed to real Apples.

Cultivars
Needs info here