There are a lot of Chinese restaurants in Riga - I don't know if they are popular... I personally prefer to eat at home, not consume 3rd parties food

Just go across Valdemara street in Riga and you will find few Chinese places:
Lielais Ķīnas Mūris [Great Wall of China] - Valdemāra str. 21 (Valdemāra centrs)
Honkonga - Valdemāra str. 61
Old Shanghai - Valdemāra str. 123
There are also:
Panda - Lāčplēša str. 13
Ķīniešu Bistro - Čaka str. 110 (entrance from Tallinas)