Hi, you can easily find the Muslim Restaurant in this city.
Here is my advice:
Huatian Youyishun Restaurant, at No.28, Huangsi Dajie, Xicheng District;
Qingzhen (Muslim) Meishi Restaurant, at No.2, Zaojun Temple, Haidian District.
Or you can find a nearby Lanzhou Lamian Noddles (Halal Noddle) to have a taste. It is very delicious.