How to Make It
Season the chicken with salt and pepper. In a large enameled cast-iron casserole, heat the oil until shimmering. Add half of the chicken at a time and cook over moderately high heat until lightly browned all over, about 8 minutes per batch. Using a slotted spoon, transfer the chicken to a plate.
Add the onions to the casserole and cook over moderate heat, stirring, until tender, 5 minutes. Add the garlic and jalapeño and cook until fragrant. Add the flour, chile powder, cumin, oregano and cayenne and cook, stirring constantly, until fragrant. Add the stock, navy beans and chicken and bring to a simmer. Cover and cook over low heat until the chicken is very tender, 30 minutes.
Uncover and simmer the soup over moderate heat until slightly thickened, about 30 minutes longer. Season with salt and pepper and serve with the tortilla chips, sour cream, Jack cheese, cilantro and avocado.