The standard name for moon cakes in Chinese is 月餅. In Thailand they are called ขนมเปีย or roughly ‘khanom pia’. The first element is a general word for baked goods, so the operative term is ‘pia’ with middle tone. I recently learned that in Vietnamese they are called something similar – bánh pía, with the first element again meaning cake.
I am wondering now if there is some alternative name for moon cakes that is the source of this ‘pia’ in Thai and Vietnamese. It might come from some southern language like chaozhouhua, since the huaqiao communities in Southeast Asia mainly have their roots in the South. Does anyone know?