Heat the oil in a wok or large pan. Fry the onion rings and garlic for about 2-3 minutes while stirring. Add the carrots, zucchini and broccoli and stir-fry for 3-4 minutes until they are just tender. Pour in the vegetable stock and coconut milk and bring to the boil briefly. Fold in the soy sauce, curry paste and noodles and simmer for 2-3 minutes until the noodles have risen. Finally stir in the bean sprouts and coriander and serve immediately.