Preheat the oven to 180°C.
Heat 2 tablespoons of the oil in a large frying pan. Season the chicken drumsticks with salt and freshly ground black pepper and brown them in the frying pan, then remove to an ovenproof casserole dish.
In the same pan, fry the onion, chorizo and garlic for 5 minutes to brown lightly then add to the casserole along with the butter beans. Add the tomatoes and stock and season with salt and freshly ground black pepper.
Heat the remaining oil in the same frying pan and add the breadcrumbs, paprika, oregano and parsley and fry until it is well mixed and going a little crisp. Spread this breadcrumb mixture over the casserole and bake for 30 minutes. Remove from the oven and serve.