Preheat the oven to 180 degrees C. Heat the oil in a flameproof casserole over moderate heat. Add the spring onions and garlic and cook for 2 minutes or until the onions are soft. Stir in the carrot and celery and cook for 4 minutes or until the carrot is crisp-tender. Add the mushrooms and cook for 3 minutes or until the mushrooms are softened.
Stir in the burghul, stock, 1 cup water, the rosemary and a pinch each of salt and pepper then bring to the boil. Cover and bake in the oven for 20 minutes or until the burghul is tender and the liquid has been absorbed.