There are a number of researchers working on producing edible insulin. The first successful edible vaccine was announced in 1990, and since then researchers have developed a number of edible vaccines, including one from the University of Western Ontario that prevents diabetes. They have also transferred the technology to trying to produce insulin containing foods.The great challenge to this technology is finding a way to stabilize the insulin so it is not destroyed by the acidic environment of the stomach.
The key tool to creating these foods is transgenics. A gene for insulin production is isolated and is transferred into the plant cells, usually by using a bacterial vector technique. Once the cells are "infected" by the gene they will begin to produce the desired protein.