Located near Serangoon Junior College, at Block 703, Hougang Ave 2, the sliced fish soup here totally rocks. You can order it with rice, mee sua, or Koka noodles. They have it in tasty clear soup or Tom Yam soup (warning: spicy). You can also try the mixed seafood style.
I had the fish in clear soup with rice and the wife had the fish in Tom Yam with Koka noodles. The fish was thick and fresh, and so good, that we ordered a second bowl without the rice. The coffee shop used to have a 煮炒 stall but it closed down because everyone who ate here at night came for the sliced fish soup stall.