I found, with the assistance of a friend, California 2 hotel and bar on the river front near the harbor.
Now if you were not staying there and just walked past I doubt you would think of walking inside to eat, well you should. They serve some of the best fish tacos I have ever had, but with a little Cambodian flavor. I can not say exactly what was in the sauce that gave it that extra good taste but I can say I went back for the tacos 3 more times.
Definitely recommend finding this one.
If you are walking along the river front, with the river to your right, keep an eye out for the Phnom Penh night market and go a few more blocks. Go past the night market and keep an eye out to the left or you will likely walk right past it.
Sorry the picture is a little blurry not very good lighting in the bar.