We have been going to Nyonya for almost 5 years, and though we love it, we have usually been disappointed by the fish and seafood -- we found it carelessly cooked, and the seasonings and sauces too sweet, gloppy and overdone -- altogether lacking in magic.
We were there a few days ago with friends who were in from Israel, and who were much less interested in eating the usual street food and noodles than in having fish and other mains. So, with much trepidation, and after lots of roti, satay, achat and lobak, we ordered steamed sea bass in Nyonya special sauce and also chinese broccoli with salted fish. Both were marvelous.
The fish steamed just right, fresh (they have tanks), sweet and delicate, and the sauce was a wonder. It was a brownish red thin, brothy sauce with over and undertones of lemon grass, chili, blanchan, curry leaf, coriander, tamarind and surprisingly (but wonderfully) fresh mint. I have never had their assam fish head casserole, but this is what I would hope it would be like. The only complaint is that they serve it on a platter over a flame so it kept simmering, but we enlisted the help of the waiter in rescuing the fish from a second death.
The broccoli was also great, and it almost makes me wonder if this is the real origin of the chinese broccoli with crispy pork that seems to have gone into decline at Sripraphai (the large dry meat problem). The stems are cut into thinner sticks, and stir fried with thte leaves, garlic, and lots of salted fish which were dry brown slices that could easily be mistaken for roast pork , by sight (though not by smell)!! This is a great dish, which marries well with mounds of rice. Just be sure to have gallons of water handy for your trip home.