Toa Payoh Lorong 5 Food Centre seems to be the supper spot for many people. Some of the stalls operate past 12 midnight such as He Jia Huan Ban Mian.
The prawn noodle soup was the traditional Singaporean kind, sweet, slightly prawny and really quite subtle. Although recommended by ieatishootipost, this was really a so so bowl, such that I didn’t finish the noodles. Only opened at night.