In a large enameled cast-iron casserole, heat the olive oil until almost smoking. Season the pork cubes with salt and black pepper and add them to the casserole. Cook the pork over high heat, stirring once or twice, until lightly browned in spots, about 5 minutes. Add the onion, green chiles, serrano chiles and garlic. Cover and cook over high heat, stirring once or twice, until the vegetables are softened, about 5 minutes. Add the chicken broth and bring to a boil. Cover partially and simmer the stew over moderately low heat until the pork is just tender and the broth is reduced by about half, about 20 minutes.