Instructables member TimAnderson has a great HOWTO for growing molded "portait gourds," a technique from China and would work with other vegetables. He starts with a 3D sculpture of his subject, creates a mold, and then coaxes the veg to grow within the mold's constraints.
This mold has a flexible rubber lining which makes it easy to remove from the gourd. A plaster mold adheres to the gourd more tenaciously and usually the mold is destroyed in the course of removing it from around the gourd.
The gourd is then allowed to dry slowly, and the outer coating called the "cuticle" is removed. Then the finishing steps, if any, are done.
On this gourd, the details of the face and hair were then traced with the point of a jade knife to enhance the detail, It was dyed with dark tea, and a coat of varnish was applied to make it shiny.