In a large pan, over medium heat cook onion, garlic, ginger and crushed chillies in oil for 2 minutes. Pour in stock, carrots and celery and bring to the boil. Reduce heat, cover and simmer 5 minutes. Stir in peas and prawns, cover and cook 3 minutes.
Break noodles into 2 inch pieces and stir into soup; cover and cook 3 minutes more, until vegetables are tender and prawns are pink. Stir in soy sauce, pepper and serve.