Peel the chayotes and cut them into 1/4 inch julienne, including the core and seeds. Set aside.
In a blender jar, combine the tomatoes and garlic and blend for a few seconds, until fairly smooth. Set aside.
In a large heavy skillet, heat the oil over medium low heat. Saute the onion with the whole chiles for about 2 minutes, without browning. Add the tomato garlic puree and continue cooking, stirring and scraping the bottom and corners of the pan for about 3 minutes, until thickened and reduced. Add the chayote, water, and salt. Cover the pan and cook over medium heat, shaking every so often to prevent the chayote from sticking. After 10 minutes, add the epazote, cover the pan again and cook for 10 to 15 minutes more, until the chayote is softened but not watery. Serve immediately.
To roast a tomato, heat a dry skillet or griddle over high heat. Roast the whole tomato, turning when the bottom is slightly charred, until it is golden brown with charred patches on all sides, but not burned (the flesh will be quite mushy). Leave the skin on.
c.1997, M.S. Milliken & S. Feniger, all rights reserved