Place noodles in a bowl and pour boiling water over to cover. Set aside for 5 minutes, then drain and set aside.
Heat the oil in a wok over high heat. Add the garlic, onion and chilli and stir-fry quickly for a few seconds. Add the prawns and cook for 1 minute, then add the fish sauce, sugar, lime juice, egg and tofu.
Cook, stirring, for a further minute until combined, then toss in the coriander and beansprouts.
Pile into serving bowls and garnish with peanuts, onions and fried shallots.