heat a large saute pan on high heat, char the tomatillos until they are blackened all over. chop tomatillos including skins and seeds. In a large stockpot, heat oil over medium heat, saute onion, chayote, potato and bell peppers until wilted. add jalapenos, garlic, chiles, tomatoes, tomatillos, stock, water, salt, and spices. stir, cover simmer 30 minutes. in a blender puree corn chips with 1 cup of stew. add pureed chips and black beans to stock pot. cook and stir for 15 minutes. to serve ladle into bowls and garnish.